Ooo, nice...
I'm hopefully going to take Biology and Chemistry too, as I'm aiming to go down the veterinary path. Also fingers crossed I'm going to take maths as that may help, but I think just biology and chemistry is alright for a few universities (you would probably want to research that yourself or someone more experienced on TSR just to check).
For a 4th a-level, I'm graphical communications would be nice as hopefully it will be a semi-relaxing subject that I can enjoy, even though it has no relation into the veterinary career 😂