When I was doing some great bushwhacking backpacking trips my regular partner and I carried Ridgerests. Never worried about them. Sometimes they were carried as a big open tube lining our packs, sometimes rolled tightly and strapped outside where they got fairly shredded sometimes.

I think the corrugated Ridgerest is more comfortable than the harder smooth stuff. But it takes up more space. For camping on snow one of each would be good.

A 3rd occasional partner carried a Thermarest. He had a bad night when the mattress sprang a leak and he had no patch kit (nor would that have helped at 0200 in the dark woods). We DID have a big lump of white open-cell foam that some careless camper had left in the woods that we'd policed up to carry out when we broke camp so John stuffed that chewed up foam under his tent floor and made-do. (brief story here: http://estes.on-line.com/rmnp/reports/teratomah.html)

Learn what you will out of that.