Welcome to the board,,
Sounds like you learn the hard way the first lesson of float planes,, they stall quick with all the drag and extra weight of the floats.
Shouldn't be hard to set up the Alpha on floats,, I don't have one, but looking at the specs a set of 30" floats should do ya fine. Plenty of knowledge here to get ya going. Jim will be along soon to recommend Foam Floats
,, Not a bad idea for that that smaller size plane,, keep it light as possible and it will do well,