hey I'm in U6 and I applied to medicine (firm choice is st Andrews):
- most, if not all, uni will ask for chemistry and at least an A. I haven't come across a UK uni that doesn't ask for an A in chem
- Biology is incredibly useful, quite hard work but if you're into medicine it will give you some essential foundations
- most unis ask for chemistry plus one other science, this can be maths/physics/biology or some accept psychology as a science, they will specify if they do or don't. but if you're not sure email admissions
- if you're on the fence about maths, *don't do it*, just some personal advice. maths this year has been a bit of a disaster. I was really confident in GCSE maths and I did ad maths as well, yet U6 maths has just been very difficult. if you want to spare yourself, definitely take psychology instead.
- some uni like your third to be a humanities (e.g. Brighton and Sussex) but that's not necessary if it's not your thing
personally I am taking chem, bio, maths and PE. PE has been a godsend as it's biology but a bit simplified plus some basic movement physics and some history/politics which makes it interesting.