M.H.
my son is big for his age and i struggled with the same thing... i ended up getting him one of those potty seats that sit on top of a normal sized toilet ... i got ours at kmart, it has a hook for the wall and a ring attached to the seat to hang it up so u dotn have to touch it and stuff. my son loves it(still doesnt really go potty on it yet but hey its a start)