For all of the potential courses, maths is essential and taking further maths would really strengthen your mathematical ability and make you a stronger candidate for these courses. They all require a logical mind and so your subject combination at A-level should reflect this. Mathematics courses all need mathematics and for places like Cambridge, you also need further maths. With economics, mathematics is looked upon very highly and essential at top unis such as LSE, where they also name further maths as desirable. The decision modules within mathematics A-level provide some insight into computer science and so if you do one of them and enjoy them then this could be a potential pathway. With PPE, unis want a combination of traditional subjects with a science/humanities mix. They do not have specific requirements but A-level maths would be very useful for the logical side of philosophy and the mathematics involved in the economics side of the degree.
I'm currently in year 13, studying maths, further maths, physics and DT with an offer from Oxford to study engineering (another maths related course open to you if you also take physics A-level) so if you have another questions then please message me. When choosing my A-levels I initially took english lit in place of further maths and after a week I was sick of it so I choose further maths as I knew it would help with what I would like to pursue in a science/maths related area, so your choices aren't set in stone and you can change if you don't enjoy them. I've been through the whole application process and decision making between a degree in maths, physics and engineering so I can send you some resources that helped me decide.