As long as you don't think you're too smart for homework and practices, then Further Maths shouldn't be a problem. To score 90~100 for Add Maths, you don't really need to do that much exercises as compared to Further Maths. Currently doing Edexcel A-levels, covered a few chapters in the Further Maths modules and I find it okay.

Maths itself is like an advanced version of add maths, especially the A2 parts. My lecturer basically told us to do most of the exercises in the textbook, then after finishing the syllabus we would do other papers like past year papers. It depends though, my lecturer was awesome ... not sure whether would I understand without his guidance.

I have no interests in sciences >_> maybe it's just because I'm lazy