I have a Slumberjack with Holofill II it seems to work down to 35 or so fine. (works on colder nights by wrapping it in a quilt type blanket) It’s going on 20+ years old and still holding up well, not a single problem with it and I do a lot of camping every year. It’s rated for +20, but I never used it when it was that cold. I run it through my washer a few times a year (on gentle cycle) to clean it. I also use a pad under it to keep heat in and to soften the ground somewhat.

I don’t know if the model I have is made any more, but considering how well it’s held up I would buy another Slumberjack.

I think it was like $30.00 when I bought it, it was so long ago I can’t remember for sure.

SlumberJacks are still fairly inexpensive for the quality. I think I paid about $70 for the one my wife has.