Please, please, please find a local store that sells the beach style (same as the Disney ones) and try them on before ordering.
Even that isn't perfect, because sometimes sizing is different within each size. I have two Med pairs (I wear an 8) and one is at least a 1/2 size bigger than the other. I ordered a pair of the Disney ones yesterday in Small, because the ones I've had for a while are bigger than they use to be (and i think smalls look less huge). They mold to your foot after a while and sort of spread out. That pair is just as comfortable as my other ones, but I'm hoping the small will look better (HA!)<--especially since I got the bright red clown shoes style!
So, you'll probably fit into a medium on the big side and a small on the small side, but it's best to try them on somewhere first.
ETA: I assume you're asking about SM, Med or Large since the disney ones I ordered came in those sizes and not actual sizes. I have a pair of Beaches that are 8s and they fit me the best, but still on the big side.