The Thermarest NeoAir is an amazingly light inflatable camp mattress that has a relatively good R rating as well. Its triangular baffles that run from side to side make it stable to sleep on.
The small size makes an ultra-lightweight component for a minimalist sleep system.
Out of the packaging its about the size of a drink bottle:
The small size which is 51cm wide and 119cm long, weighs 255g. The supplied stuff sack weighs 14g.
Once inflated, its about 6cm thick and feels very comfortable and surprisingly warm for an air mattress. For the foot portion of my sleep system I use the back protector from my Gossamer Gear Mariposa Plus backpack.