I've used a quilt and don't mind them if it's above 50F.

I have the Montbell Super Spiral Down Hugger #3 (800 down, 30F, 21 oz). I really like the comfort, but haven't overnighted with it yet. It's nice because you can have the freedom of a quilt with the draft protection of a bag. And, it works great as a quilt when unzipped.

I hear these are rated a little optimistic, so get the #1 (15F) for 20F temps.