I'm relatively new to the hammock hanging concept. I've been experimenting with a variety of configurations for warmth. I was very pleased with what I came up with this weekend. The temps got down into the mid to lower 30's it was also very windy. I used (2) 3/4 lenght Therm-A-Rest Ridgerest pads and a synmat 9 DLX air matress. The pads are 48" long; one pad went down at the bottom on top of the air matress, it came up to slighty above my waist, the second pad was wrapped under the air mattress; this prevented movement (make sure there is some overlap with the two pads, or you will know it). The second pad is laid purpendicular to the first pad, it will come out on both sides of the top of the mattress allowing at least 12" exposure on both sides giving you plenty of padding to keep your shoulders really warm. I did have to tie the pads to the bottom of my backpack because they take up a lot of room inside the backpack, but I felt that was a small price to pay. The two pads together weighed a little less than 1 lb. Oh BTW the two pads when rolled up together, will make an excellent seating pad!
My air mattress is a bit on the heavy side (but it's all I have right now), it comes in at 2.5 lbs make sure that you don't over-inflate it, it needs to be on the limp side. I never slept so well in such temperatures. I was actually very warm, I believe it could have been even colder and it would have still been very effective. I had tried using each of these items separately, but the pads by themselves were ok, they would shift constantly, the air mattress by itself was still cold on the bottom and my shoulders were very cold. The two together were a dream come true.
Hopefully someone else will give this a try and we can continue to work on it, this is a great start. I am considering a space blanket on the very bottom my next time out.