I'll second the Costco quilt, if it fits (length.) If you didn't want to sew a footbox, you could use safety pins to create one for a trial run, then get it sewn if it works out.

When my wife and I bought ours a few years back, they came as a set of two for about $25, including two small stuff sacks - if they still come that way, having two gives you other options for making a liner by sewing them together with or without a zipper. (Availability may be an issue: I couldn't find them on the Costco website today; I think they come and go depending on re-stocking.)

We use ours to wrap around us while we're sitting in the living room on a cold night, but it's not cold enough to have the fireplace on.