which A-level combinations should I pick?

Yh first off dont get into med if you are not interested, you dont want to spend your entire life doing a job you really dont like just cause it is said to earn a lot of money, besides there are a lot of broke doctors. Only the ones actually enthusiastic about the job get the money. Also for med you might have to pick up biology as well.

And personally i recommend 3 a level subject, i am currently doing just 3 and its stressing me out. Especially since you're are interested in more writing-heavy subjects, you might want to do 3 subjects so you focus entirely on them and not having to stress about an additional subject that might not do anything for you. Trust me the fourth subject is always pretty useless, a lot of people always end up dropping a subject midway.

For your subject combinations i think you should choose the field you are interested in getting into (if you dont know yet like i did then, i chose the subject i enjoyed the most and built my subjects around it. so my favorite subject was computer science so i did my research, i went to various universities and searched up the computer science course and checked the requirements, math was a requirement and any science subject. so i came to conclusion that i would do computer science, math and physics and i went to the guidance counselor at my school for advice and he agreed with my subject combination.

If you want to do art and also pursue business incase art doesn't work out, you can do ;
Art, math and business studies or economics (if you want an additional subject, you can go for English language or literature)

But if you are maybe more into psychology and med then you can go for
psychology, bio, chem, math (if you are going into the research part), English language (if you are not)
You can get into fields like: clinical psychology, neuropsychology, psychopharmacology or neurochemistry.

GOOD LUCK!!