Just to add, if you get the fleece blankets sew them up across the bottom ans about a foot up the side.One for single,two for a double.Slip these in side your sleeping bag,If you are still cold put another fleece blanket on top of the fleece blanket, so it is not on the outside of the sleeping bag.I did this when it snowed last november and was not cold.
I used to be freezing at night, even wrapped up in t-shirt vest, long sleeve t-shirt and polo neck fleece on top half and track suite bottoms and socks below - and this was May! This was on a normal airbed and just a sleeping bag.
Now I have a very thin silk sleeping bag liner, use a space foil blanket, as mentioned in previous posts, and a normal plastic backed picnic rug on top of the airbed.
Now I sleep in just a long sleeve t-shirt and nothing else - same sleeping bag too. just goes to show how changing 3 little things made a MASSIVE difference. Hardly any extra space taken up either.