well yes and no - I would not discount a proper sheep (not small lamb) skin, wattle tannned, short wool - 15-20mm clip.
They are soft and supple and lighweight and great insulators. Dont burn if near a flame, don't lose air. Don't need inflating. Always immediatley at your service.
I'm not saying modern sleeping mats are inferior, just offering an alternative.
Carbon footprint probably less but do they pass wind??

Sheep ie
Try wrapping a sleeping mat around you to keep warm. It doesn't conform like a sheepskin and the extra warmth is fantastic.
You can wrap it inside your pack and then place, stuff or however you pack the pack gear etc inside that.
OK I'll admit get them wet and that's not nice.
But then that applies to most stuff we cart about the bush.
Exped Down does looks good. How long do they last in real use in bush?
There are some comments here you may find useful
http://bushwalk.com/forum/viewtopic.php?f=15&t=7081