Welcome to the forum Ben.
We have a Roman Big Brother Hood Sleeping bag with a rating of -10 and you can unzip them completely open as we use ours as a doona on our bed in the campertrailer. Our son also has one the same he uses in his swag and he has slept outdoors with no cover in -6 degrees and woken up with frost covering his swag but he was as warm as toast.
We bought all our kids King Single swags and they have been worth every penny. The girls sleep on the floor of our CT (softfloor) in theirs and in winter we put yoga matts underneath them and they sleep with water bottles. The swags are used quite often at home when we have visitors as well as the kids taking them to friends places for sleepovers.
But like Gypsy said just do a search and you will get heaps of info from other threads also.
Looking forward to hearing how you got on....