While shopping for a bed I ran across this:
http://www.ikea.com/us/en/catalog/products/80282326/
Might be a good option for those who want a little cushion to sit on. I didn't have my scale on me, but this thing was featherweight, I'd be astonished if it was over an ounce. This is a lot cheaper and probably lighter than similar expensive sit pads Ive seen.

