My DS only used a potty for a short time but one thing I would look for is one that is sort of wide, basic ones are the best I think! We had a fancy one with the backrest but he found it awkward to get on and off, we have a friend whose little girl couldn't' even get her legs in it, she wasn't huge but it was really tinsy. DS went to a seat on the toilet pretty quickly and even then progressed to just the normal toilet with an Ikea step really quickly. I would consider one of those steps things as well and a cheap basic potty in the interim.