Is this for at home or to take somewhere else (like preschool)? If it's for home, you can make a large pillowcase bottom, then insert a king size pillow. If it's to take somewhere, you can make a thick quilt and then fold it (maybe zipped or snapped together), for the bottom. The top could be attached down the middle, so that when the bottom is folded, it covers the top side. I can "see" this in my head but am probably not explaining it very well.
