In reply to Jones_88: My ultralite thermarest is more comfy when used alone than my ridgerest (and full thickness thermarests are just luxurious) BUT alpine bivies can be very rough and I wouldn't fancy the chances of a thermarest on those rocks. Better go for a ridgerest or multimat. As they aren't too expensive consider also then getting a three quarter length thinner thermarest (or Alpkit clone). For camping on grass for example the thermarest will be more comfy, but then used together you will have a system that will insulate you when snow camping down to at least -27. It might work for colder weather but that's coldest I've slept out on my mats!
By the way, I have 20 year old thermarest that I still regularly use, and my ridgerest is about 15 or 16 years old. They might seem a bit pricey over cheaper copies at first but if you are a regular user you'll get your monies worth from them.