Cold enough that sleeping in an open bivvy is difficult. But if you pick better spots than I used to you can get quite a bit warmer with the same bit of kit. The more walls and preferably some kind of roof the better.
Avoid the mountain top, avoid the bottom (ooh nurse) and stop where you'll have to start with a climb rather than a descent or you'll freeze even more.
Sleeping pads/mats definitely help.
I have plenty of my own insulation so I can get away with a bag cover no bag.
Some people use just a bag (Lael in TABR), others will use both and a silk liner.
It depends how you feel the cold and how much you plan to sleep outside.
Cold enough that sleeping in an open bivvy is difficult. But if you pick better spots than I used to you can get quite a bit warmer with the same bit of kit. The more walls and preferably some kind of roof the better.
Avoid the mountain top, avoid the bottom (ooh nurse) and stop where you'll have to start with a climb rather than a descent or you'll freeze even more.