Don't go into medicine just because of the money - it is a long hard road to get to the point where you're earning a decent salary, and the stress/ poor work-life balance etc. means you can't really just sit back and enjoy the money you do get... I used to also have the idea that I wanted some super high-paying career, but as I've gone through uni I've realised that that just isn't for me, I'd rather get an average job and have time to enjoy my life
It sounds like you are more interested in humanities subjects - despite everyone stressing about the lack of job opportunities etc. there are a LOT of graduate jobs which will accept anyone from any degree background, e.g. marketing, finance, business, consultancy (there's the money...), teaching, etc. and loads more. If you're particularly interested in writing, there are jobs in journalism, creative writing, marketing, etc. which all have a high component of writing. Generally only technical careers like engineering, scientific research, medicine, dentistry, etc. tend to be very specific with degree subject requirements.
I'd recommend trying to get some work experience in things like business, marketing, museums, schools, journalism etc. to try and figure out what kind of career you may be interested in.
In terms of A level subjects, just pick those you enjoy and are doing vaguely well at at GCSE - e.g. History, Politics, RS, English Lit, English Lang, Art, anything like that
Try and have a few "facilitating subjects" (the more "highly regarded" subjects which keep lots of options open - e.g. History, English, Maths, these kinds of things) because sometimes these are looked on more favourably by universities.