If you want to keep your options as open as possible, having a science and maths is a good idea. RMPS showcases a similar set of skills to English, Modern, and Geography, so is less likely to add to your uni application.
Spanish could also be useful, so an alternative would be to pick that and Biology and maybe do maths in S6 once you have a solid set of results in the bag.
Have a look at unis and entry requirements, most only specify grades for your top four highers, so if one grade is a bit lower that should be fine, but if you are going for a course that routinely asks for five As you might be better going for a safer set.