My little lady and I bought matching mummy-bags rated for -30°C. These bags are designed for winter hiking / tenting / mountain-climbing - so they pack down to a very small size for travelling.We got one of the sleeping bags. They had my wife's size but not mine. We opted for -20 C bags since we're going to be indoors and have a least a mild heat source to keep the house warmer than the outside world.
What we do is open them up - zipper the sides together and then climb into the bags. Shared body-heat works very well - and - if things are extra cold (we winter-camp as well) then we have a couple of spare blankets and we pull on our balaclava's ..
We got our sleeping bags from "Campers Village" which is an Albertan company.