I just did AFM this year, getting the A* isnt as hard as it seems
My UMS for all 18 modules was : C1 - 95, C2 - 99, C3 - 100, C4 - 100, FP1 - 95, FP2 - 100, FP3 - 82, M1 - 98, M2 - 96, M3 - 96, M4 - 73, M5 - 78, S1 - 100, S2 - 89, S3 - 86, S4 - 92, D1 - 88, D2 - 16
So you can see there is room to mess up a few modules and still get 3A* in maths, personally i think the easiest A2 FM modules to get 90+ in are M2,S2,S3,S4,M3,FP2, I wouldn't say im exceptional at Maths too (got 1,3,2 in STEP I,II,III)