yep sounds like you are doing bindings up as tight as will go but still not tight enuff So either
a/ put something between footplate and shoe, as suggested a flip flop sole, or similar firm closed sell foamy plastic
b/ thicker/chunkier shoes.... big sk8er trainers
c/ put some padding on the binding straps, if im using extra thin shoes such as converse, i fold up a tee shirt and place on top of foot b5 doing bindings up