I'm thinking about applying to medicine as well (just finished GCSEs). I've chosen Maths, Chemistry, Biology and FM. Chosen these becuase I know I will enjoy these at A-level and will do well in them as opposed to other subjects. Just go for the Uni requirements and the subjects you will enjoy as you'll find them easier to do. Then you can get them amazing grades as opposed to people with "non-soft" subjects who are doing them because they think it'll get them in. I was always put down by a friend who claimed to be doing "smart" subjects at GCSEs and said that because I had one DT subject, my subjects aren't "smart" (yet all our subjects were the same - 1). Little does she know I have an A* in that "dumb" subject (since it was coursework and controlled exam) and she was struggling with her "smart" subject (our other subjects were exactly the same).
Just do Psychology as Chemistry and Biology are the main subjects and anything else really doesn't matter.