Nice to see a thread on woodworking , unlike you I mostly do restoration of antique hand tools like Stanley planes and socket mount chisels .Anyways , from what I've seen on kotatsu heaters it's basicly a heat lamp bolted to the bottom of the table. For the fabric I'd use polyester , it tends to shrink away from the flame and self-extinguish.If you want to keep with the Japanese furniture try a tansu , it's a Japanese version of a chest of drawers.