You know, i just took my a levels, and i am studying them now, Further Maths, Maths, Physics and Geography, because i enjoy them. I took these myself with no advice from here, and i love them.
Just further maths isnt for the faint hearted, In my group we have finished studying Core 1, half way through Decision 1 and half way through Stats 1. All in about 7 or 8 weeks. And about 6 people have dropped out. I would say if you got a B or a low grade A take normal maths, however if you got a high grade A or A* then go for Further. If you think you can. [Hope this made sense!]
Just do what you like! And also guys, many people say a degree is irrellivant, many others say its crucial, so to put another opinion in there, dont do a degree, its more debt, when if you succeed at flying then its a waste.
Follow your heart, not your mind!
Just my 2 pence!