...well, I've made a Prince costume... so I can tell you what I did, perhaps? For the head I used plastic corset boning
(Purchased from here, if you care to know.) which I then bent into shape and taped together with just simple duct tape. I just made several circles and then began to tape boning down to connect them all until I'd made a little cage.
I took a picture, too. After that I wrapped quilt stuffing around the head to make it nice and squishy
(Just hot glued it down.) and then put the fabric over that.
As for the clothes... we used a pattern for a maternity dress since it started smaller at the top and then got nice and large at the bottom, and we put some more boning into the bottle of it to make it stick out right. I would suggest finding a pattern for some pajamas that have footsies for the bottom of the Prince... I tried to wing it and make my own and failed pretty well. *chuckles*
I don't know if that's any help or not... since the thread's a little old.... but.... *shrugs*