How do I make a peach costume?

Hi, I'm dressing up as James and the Giant Peach well the peach with James on top-it's complicated. Anyway I need to make the peach like out of a polystyrene ball that I can wear or something but I don't know how to make it or what to get to make it? Paper mache? Giant plastic ball? Any ideas for the actual peach welcome but not too complicated :D. Oh and I need ideas quickly because its for Friday, so please help! Thanks, xx