find this thread interesting, esp. since i'm not a stomach sleeper. always like to learn something new.
1) Daniel, Gossamer Gear has both 1/8" & 3/8" thick foam padding. look at their ThinLight product (FYI - the drop-down list selects which product you are ordering).
they also have a NightLight, "egg-crate" cut, foam pad, but this might be overkill except in the very cold. the sectioned torso-length NightLight is my primary pad. i find it quite warm for down to freezing. would work a bit lower, i believe, but i can't personally testify to it. i had an email fr/GG that GVP uses the NightLight at 25deg on top of the snow w/only his bag & no other shelter. i forget what the email specified as to his clothing, but it seemed, to the best of my recollection, that it was a typical winter UL 3-layer system - nothing too exotic.
2) David - due to my slight medical background, i find comments like yours (viz. lower BP for stomach sleepers) very interesting. can you please direct me to a source so that i could read more? would seem to me that the BP's would be quite low in either case cp. to let's say when one is strongly exerting oneself (systolic can really spike, like up to 170 during a lift - when i was much younger & training for power lifting competition), & even a bit lower than one's normal waking BP while sitting. i've never read/learned anything about BP while sleeping, so i would appreciate any further info/direction you can provide.