When I got in to backpacking in college I was a ground-dweller - for a couple years. So I have all the gear. I combine a Therm-A-Rest inflatable with a blue closed cell foam pad underneath. Extra cushion and a deflation backup.

Although... I might actually try 2 foam pads. I have another one that has the egg crate pattern (cheapie, not an accordian fold therm-a-rest). The egg crate pattern I've had for others that don't have gear, so I've actually never used it. However, I dislike the inflating and deflating of the Term-A-Rest pad I have. By layering the 2 foamies it would be a matter of unrolling and rolling back up. Less time and fuss. As to comfort - not sure on that yet. I'll have to experiment on that one. I think the egg crate pad will be softer than the blue closed cell pad so layered together might work OK.

I slept in the bivy and my bag liner last night, just inside, and it was fine. However, it wasn't cold in here so there wasn't a big temperature difference. I am thinking the condensation issue would occur with a wider temperature difference (cold outside - like 50's or lower). I'm not sure what the threshold is on the temp vs condensation, but that would be nice if I can get down to freezing without condensation in the bivy (not likely). I've used the bivys before, but I didn't pay much attention to them from a technical perspective - just that I got condensation in them at night. The silver one was on a winter backpacking trip (around and a bit above freezing) - got out of it 1/2 way thru the night from the condensation (had other gear with me in case that experiment went south, luckily). The orange one I used in my hammock in cooler weather in the summer once. From what I recall I had condensation in it also. So I suppose I can try it and see what happens. It weighs next to nothing, so not much "weight".