Hi AcornFalls. I'm a mature student who is re-entering University at age 27 having made a wrong turn the first time around. I hope I can help in some way, even if it's only to give you food for thought.
I would say that what you should pick entirely depends on what you intended to do at university, and in turn what you intend to do post-university. If you don't have an idea of this, it's a good time to start thinking seriously about at least a few potential careers. Trust me, it's a bad idea to put off thinking about this until after your A-Levels. I know it sounds simple, but a good tip for life in general is to plan several years ahead. You can always change plans you make, but you can't take back wasted time.
If you do already have an approximate idea of which University courses you might be interested in, then it's very easy to find what they require in terms of grades (I can help you out on that front if you want a hand). Putting the effort in now, and going the extra step and planning your future will save you much doubting and heartache, and will put your mind at ease in the present, and allow you to feel more motivated and thus get better grades.
A few pieces of advice regarding subject choices:
1) PICK MATHS. FOR THE LOVE OF GOD PICK MATHS. Maths is the darling of universities and employees. No A-Level is treasured anywhere near as highly as Maths. I personally have come to seriously regret not taking it. It opens the door to every science and engineering subject out there at University level and beyond.
2) I personally would advise against studying English Lit/Language unless you are planning to go on become an academic or similar. Having been through the process, I'd recommend that the subjects you take now are ones that give you recognisable and transferable skills. This is coming from someone who got 92% in their A-Levels in English, and then went on to study American Literature at University. So it's not like I don't like the subject; I just that I don't think it's all that useful in the long-term.
3) Learning any language is a good idea. All languages are highly regarded and will be good for University applications and for your career - so long as you persist with learning them to fluency.
4) I also did History, and I would say it was highly fun and gave me some transferable skills. If I had another go, however, I would have gone for Sciences instead. In general, I think Sciences are more valuable with regards to teaching you things that you can go on and immediately use.
5) Finally, I would like to point you towards Philosophy and Psychology, which are both superb subjects for self-improvement, and for expanding your mind and intellectual capacity. I would personally recommend you take either or both of them. They can also be an absolute blast to learn.