Maths art and bio are good choices. However, it's worth thinking about whether you want to take art or if you want to draw for fun. There's no reason you can't do both, but taking an art A level is a lot of work and if you don't intend on going into the arts I'd recommend drawing in your own time loads, enjoy it, but taking a different subject. That being said, I've found the art A level a brilliant opportunity to grow as an artist and try new things. It's also something completely different to your other subjects. Art is, a lot of the time, about expressing your interests, and it can be in a more academic way than you may think. Biological drawing, artist research, the mental capacity it actually does take to make good art... It's a good subject. It is coursework heavy though. I think it would be manageable alongside your other subjects though.