Cut hoola hoops to fit the internal diameter and use squirty insulation foam to hold them in place. Take the mattress topper and cut it to the size you need. Hot glue the seem down the short side of the mattress topper or use spray glue. Tape the seem in place until the glue sets. It requires a certain level of skill to use an air-brush for painting but you can easily do it by viewing some videos on black panther costume YouTube.