In reply to jondo:
depends why you are going to do it, if you plan to climb the next day and won't come past your bivi site or a kit dump, then going light but a little chilly at night is the usual trade off. You can of course bivi like a king, sleep like a baby, but then climb with an anvil on your back the next day. Nearly everything in the alps is a compromise, speed versus weight or comfort etc..
I've sleep with full thermarest, bivi bag, sleeping bag and been toasty all night, I've also 'tried' to sleep in a duvet jacket and my legs inside an empty rucksack. It's finding a mid point that's key.
Post edited at 14:06