To be honest San I have no idea. I'm actually the same size as you most of the time (occasionally I will take a 2 or even a 0, but usually only in brands that run big like AT and BR). We are different body shapes though and I know you say you have a very flat bum, so it's possible that I could possibly fill out the 4's. I guess we'll never know! Too bad because I really had my heart set on getting a pair, but I can't spend even $1 on clothes at this point.