Use a plastic tote for a litter box. Gives the cats much more room. Also on this site be sure to read about the near perfect litter; chicken feed layer crumbles as a scoopable clumping litter alternative! It WORKS! litter box -- maybe a lid?
Indoor Kitty Hideout- Cats love boxes, so most kitties wiil love this inexpensive indoor hideout. Just cut a cat head shape door in a clean box, cover in contact paper to dress it up, add a comfy blanket and you get.