I've made this costume, and boot covers was the way I went. I used double layers for stability and a good, cartoony-looking shape. The shoes they went over were very square-toed and clunky. It was cute, but really silly looking, which I hear was perfect.
if you give me a dollar I'll let you stand over there and talk to me via sign language. if you want a hug, I want a Corvette.