Hi, I'm in Year 12 and I take Maths, Further Maths, Economics & Physics, and want to study Economics at university (probably Cambridge or LSE). Like you I had very strong GCSE marks (I got 93.75% in Edexcel GCSE Maths and 98% in FSMQ Addmaths). While I'm only in Year 12 (and so I've only seen the AS stuff, I haven't got onto the Year 13 A level content yet), I'm not currently finding the Further Maths content very difficult (the last paper I did with college I got 75/76, mostly AS further maths stuff), like any other subject, if you revise it enough, you will do well. Further maths probably will be difficult (and you also have to bear in mind that a lot of the very best students in the country will be competing in that exam), but I'm sure if you're willing to put in the hours then you should be able to do well
Just as a side note though, I strongly advise against taking business and economics, as business has significant subject overlap with economics, but is generally considered a lot easier, and there are some universities who won't like an applicant with business and economics (as they are so similar), so I advise choosing a different A level than that. Physics, chemistry, computer science, geography, politics and history will all complement maths, further maths and economics, but to be honest it is entirely up to you. Just bear this in mind.
Good luck with whatever you take