A very good combination, as you want to do maths in uni, would be: Maths, Further Maths, Physics, History, and G&P would be the extra AS....Doing further maths at uni would strongly benefit you for Maths at uni.....
Not to be biased but I knew someone who had 5 strong A's at AS in Maths, Economics, Physics, Biology, Chemistry and he was a really sociable guy but got rejected from Oxford for Maths, probably because he didn't have Further Maths.
Further Maths shows you have desire to do the subject to study it more and can be a strong sign of your interest in the subject. I would strongly recommend you to take it