If you're looking for the straw mats that they use in Japanese homes, well I don't think you can find them in retail. They're usually custom-fitted into homes. I do know that there are straw mats in Daiso/Japan Home/88-peso stores though! They're about as big as your average banig. They have that ricey stink to them when they're new, and they're a bitch too clean. But after a few days or even weeks, that same stinky smell isn't so stinky anymore and it actually helps make a room feel more homey.
Futon? Just put your mattress on the floor.
Futon? Just put your mattress on the floor.