I always use the disposable foil cake pans. They are shallow and cheap. I put newspaper in the bottom because my kittens were not happy with the feel of claws on foil
I also use small shallow baking pans (they don't mind the foil at all) with Yesterday's News as litter. Have fostered many a 5-week old and they seem to take to the shallow pan easily...also although Yesterday's News is meant for ferrets...it is non-clumping & dust-free for the little ones.
I have a small kitten litter box with Yesterday's News. Now since mine are about 5 weeks old they seem to scoff at the kitten box and prefer to pretend they are grown-up and use mom's!