Get a 0⁰ up to -20⁰ sleeping pad so the ground isn’t sapping heat from you, wear warm clothes inside of it, and be ready to do some situps in the middle of the night to trap some heat in there, and you should be good. Personally, if I am going to be camping at any temp below freezing, I’ll go for a zero or -20 bag since I have one, but a good sleeping pad and fleece base layers add a lot of protection whatever bag you’re in.
Get a 0⁰ up to -20⁰ sleeping pad so the ground isn’t sapping heat from you, wear warm clothes inside of it, and be ready to do some situps in the middle of the night to trap some heat in there, and you should be good. Personally, if I am going to be camping at any temp below freezing, I’ll go for a zero or -20 bag since I have one, but a good sleeping pad and fleece base layers add a lot of protection whatever bag you’re in.