Should I take further maths A-level?

I am currently considering taking biology, physics, maths, and English for my A-levels as I want to study either English literature or physics at university (hopefully Oxbridge). For GCSEs I am doing Maths and Further Maths, I got a 9 on my Y10 Mock in maths and I consistently get 100% or one mark off in my maths tests (we only started the FM curriculum a month or two ago so we haven't been tested on it yet, but I am not struggling with the content). I enjoy maths, and while I do love it, I don't have the same passion for it as I have for many other subjects.
I could probably get an A* in FM A-level if I worked for it, but I don't think I would enjoy the course much, and I would much prefer to study biology. I am aware that if I want to study physics at a top university, taking further maths A-level is probably (?) the more beneficial option. However, biology is a science so I am not watering down my options too much, and I am still on the fence about whether I want to study English or Physics in university.
I still have a while to decide- I am in Y11 at the moment, and I have applied to work experience at a nuclear energy lab for physics.

Yes, do Further Maths if you might be looking at Oxbridge sciences. Not only will it be looked upon askance if your school offers it, and you apply without it, but, if you do get in, having done FM will make year 1 so much easier. As a word of caution; FM is way harder than A-Level maths. You are competing with the very best maths pupils in the country for those top grades. There is very little correlation about being good at maths at Year 10/ 11 (which many people are) and being good enough for an A or A* at FM at A-Level. Good luck!

Aside from it being helpful for first year, do I really need it to get into Oxford? How much of a disadvantage in the application process will I be at?

There is an FOI at (physics/oxford)
https://www.whatdotheyknow.com/request/admissions_statistics_for_physic_7
I think the overall stats were something like (without fm)
applied 30%
shortlisted 12%
offers 2.5%
There obv isnt much analysis of whether the school offered it or not or ...

Oh, those stats aren't very high... I am not too confident that I can get in on those statistics- not impossible though.

I cant really see much reason for you to take biology, and if youre thinking about physics/oxford it would make sense to do further maths instead, even keeping the option to do english open.
The faq starts with "The Oxford physics course is highly-mathematical. We expect that all students who are accepted to study physics at Oxford would be capable of achieving a Grade A in Further Maths A-level, even if they have not taken the exam. It is important that you are good at maths and enjoy the prospect of applying it to physical problems."
https://www.physics.ox.ac.uk/study/undergraduates/faq/faq-admissions

That is a fair point. The only reason I am taking biology is because I really enjoy the subject and don't want to drop it. However, I don't know if I would be able to achieve an A* in FM A-level. I am smart, but I don't know how far my maths skill actually goes. I am a little slow to understand GCSE topics sometimes, but I always get them eventually. I am also extremely forgetful and often forget how to do things immediately after the lesson (not an exaggeration). I'm in top set though, and as I said I always get good marks. But FM A-level is a huge step up from GCSE Maths. Is there any way I could test my proficiency in FM A-level before committing to it? Worst case I can take it and swap it out for biology a few weeks into year 12. We will see if I even want to take physics by the end of this year!

Dont overthink a level further maths. Its not easy but its an a level and youre not really competing against anyone, youre working to get an A/A* and ~55% do. If youre doing gcse further maths reasonably well, then theres no reason why you cant do a level further maths successfully.
Biology is fairly content heavy, a level further maths is practice heavy. Choose which one(s) interest you and you think would be beneficial for uni.

I didn't realise the statistics were so high. Although that is down to the fact the majority of further maths students take it because they love and are exceedingly good at maths. That is a helpful insight though- I will consider taking it. Thank you so much!

Aside from it being helpful for first year, do I really need it to get into Oxford? How much of a disadvantage in the application process will I be at?

I am currently considering taking biology, physics, maths, and English for my A-levels as I want to study either English literature or physics at university (hopefully Oxbridge). For GCSEs I am doing Maths and Further Maths, I got a 9 on my Y10 Mock in maths and I consistently get 100% or one mark off in my maths tests (we only started the FM curriculum a month or two ago so we haven't been tested on it yet, but I am not struggling with the content). I enjoy maths, and while I do love it, I don't have the same passion for it as I have for many other subjects.
I could probably get an A* in FM A-level if I worked for it, but I don't think I would enjoy the course much, and I would much prefer to study biology. I am aware that if I want to study physics at a top university, taking further maths A-level is probably (?) the more beneficial option. However, biology is a science so I am not watering down my options too much, and I am still on the fence about whether I want to study English or Physics in university.
I still have a while to decide- I am in Y11 at the moment, and I have applied to work experience at a nuclear energy lab for physics.

I am currently considering taking biology, physics, maths, and English for my A-levels as I want to study either English literature or physics at university (hopefully Oxbridge). For GCSEs I am doing Maths and Further Maths, I got a 9 on my Y10 Mock in maths and I consistently get 100% or one mark off in my maths tests (we only started the FM curriculum a month or two ago so we haven't been tested on it yet, but I am not struggling with the content). I enjoy maths, and while I do love it, I don't have the same passion for it as I have for many other subjects.
I could probably get an A* in FM A-level if I worked for it, but I don't think I would enjoy the course much, and I would much prefer to study biology. I am aware that if I want to study physics at a top university, taking further maths A-level is probably (?) the more beneficial option. However, biology is a science so I am not watering down my options too much, and I am still on the fence about whether I want to study English or Physics in university.
I still have a while to decide- I am in Y11 at the moment, and I have applied to work experience at a nuclear energy lab for physics.

I think it's more important you find out which degree you want to do first. There is a world of difference between an English degree and a Physics degree, and you will end up wasting a lot of valuable time and effort if you persist in trying to keep both of those options open. Typically you talk about keeping options open if you are interested in reasonably adjacent fields like maths and economics, or computer science and engineering, where efforts in one subject are still helpful in the other. Physics and English, on the other hand, have too little in common for you to be able to keep up to pace with competition in both subjects simultaneously for long. Consider it this way - physics is one of the most competitive courses at Oxford (Cambridge don't do Physics standalone, but natural sciences is equally competitive) and people who are competing for those limited spots will be working continuously to achieve their goal of getting in. Are you confident that you will be able to outcompete those students if you are also trying to keep up with the competition for Oxbridge English? Do you have time to be spending on supercurricular activities/entrance exam prep for both subjects? Probably not, and little (if any) supercurriculars/entrance exam prep are transferrable between the two subjects.
But let's say you still want to keep your options open. Drop biology. It provides no utility in either case even if you are interested in cambridge natsci rather than oxbridge Physics specifically. Further maths is preferable in either case. But refer to the relevant course webpages for more information.