That seems a pretty common subject combo for med people, although strictly speaking FM isn't the best idea (since some med schools don't count it as separate from maths). But it won't hinder you.
They arent uncommon choices but they're not statistically the top pick I think geography psychology etc along with many others beat further maths to the spot of peoples fourth subject mostly because of what someone said about some unis not valuing it at all for medicine. Also a level maths is much harder than gcse so if you're not 100% sure you're a maths god don't but all your eggs in that basket
I know more people who did physics in place of further maths.
Once you have an offer you can drop however much you need/want to to be confident in making the offer. As soon as I got offers I stopped maths and further maths.