I have been pondering the same thing lately. I am more of a survivalist/bushcraft guy than a backpacker/hiker/camper. I have been using a Wally World Yoga mat for my BB, and it works great but drives me nuts that it alone takes up more room than my BB and Superfly together. Last year in for my 13 hrs in 13 degrees overnighter in my ENO DN, I used an HD space blanket on top of the pad. I am going to try just using the space blanket or even a sunshade between layers on a 35-40 deg night first.
As for all you guys using something indoors, your would freeze to death in my house or car. I guess it is my Celtic blood, I rock a kilt even in the snow.- George