On my own I would take a blizzard bag. I have one and it is a great safety aid.
I also have 2 x kisu (original design was a Karrimor Instructor Survival Unit) first one is multi person, can take 10 people and gets unbelieveably warm. Second is a 2 person. Really great for lunch as eellmas an emergency over night.
Personally though, for just me a top quality goretexnor event bivi bag, plus other kit, your chojce, but down has done me very eell, as has man made for the past 40 years, is the item to carry.
If bothying, when u turn and there is no space inside, a bivi bag is eorth its weight in gold. If in survival mode, ideal. If young foolish andb drunk, as I was on a numbef of occasions when young, my bivi and sleeping bag kept me alive on the tops, when I really should have known bettr than to go up late at night!
Alan l.