Resit or pick up a new subject?

I’ve asked this question elsewhere with no avail in receiving a response so I thought I should try here. I’m sorry for the long story I thought it might be an important factor in the decision making process. Thank you in advance to anyone who responds.
I am a 19 year old whose wanting to start university September 2026. I’ve had a tumultuous relationship with my education journey. It started with resitting my English and Maths GCSE to be able to study the subjects I wanted at the first college I attended. I didn’t fail my GCSEs but they didn’t meet the colleges requirements, after my resit however, I did. The college wouldn’t budge on letting me retake year 12 with my new subjects so I decided to apply elsewhere.
At my new college I got to study the subjects I wanted. Unfortunately because of my own inaction and not taking things seriously I ended up failing 2 out of my three subjects. The college let me continue into year 13 with the 1 subject I passed but I had to choose to other subjects to take to an AS level and no further. I did AS politics, geography and A level Biology. Year 13 went better than year 12. I enjoyed the AS subjects and continued happily with my A level. However, I must admit there was always the feeling of dissatisfaction because I wasn’t doing what I enjoyed the most.
Come to exam season, before I sat my first AS exams which came before my A level, my dad became mentally unwell. He is the sole provider to the household. He started taking time off work but that later turned into being completely unable to go in at all and therefore there was a strain on the finances. My mother could not work because she knew very little English and was caring for my younger siblings, the youngest at the time being 6. I started working to keep everyone afloat. It was full time work that I started around April, a month away from my first exam.
I managed to pull through for my AS exams, I didn’t do amazing but did okay and ended with 2 C grades. By the time my A level Biology exams started in June it got too much. The physical and mental strain meant that I completely ruined my performance in that subject. I tried to withdraw through college in hopes I don’t get a permanent bad grade but they said it was too late. I didn’t even end up going in for my last paper. I ended up with a U. I understand that it was my fault and I should have tried harder. I’ve always wanted to go to university because I genuinely enjoy learning. It has become apparent that I prefer independent learning as I seem to excel in anything I learn in my own time.
Recently my dad has gotten better and has started to work full time again so I have cut my working hours down to part time. I’ve started thinking about studying a levels independently so I can still go to university. I want to study maths and I’ve been enjoying learning it so far.
Now onto uni admissions and resits. I know I want to sit a levels in maths and further maths but I’m not sure about my third subject. Should I resit my biology? The only thing that making me question whether or not to go through with it is that a lot of universities with good maths courses, like Warwick/Imperial, look down on resits. Would it better my chances if I just learn a new subject so I am not classed as a resit applicant or would the U grade hinder my chances the same as it would if I did resit?