You will need the following things to get started.
Box (I used a Postal one, but a Cereal Box or Cracker box could also work)
Utility knife or Craft Knife
Tape, Masking or Gaff
Material (for mattress cover)
Scrap Soft Cell Foam (Mine is leftover from a mattress topper)
Step 1: Prepare Box
Prepare your box by removing any shiny tape. Then cover with a layer of tape to reinforce it.