I'm a latecomer to the thread, but for what you're suggesting (based on your later responses), you might want to look at the Western Mountaineering Mitylite bag. It's semi-rectangular, hoodless, and has two zippers (side and bottom) so you can unzip it to use like a quilt, but still leave the bottom zipper closed to make a footbox. It's a 40 degree bag, but I think it's conservatively rated. Sleeping in longjohns (top and bottom), down booties, down hooded jacket, down pants and maybe down mittens, on a Thermarest Prolite 4 pad (3/4 length), in my backyard, I stayed warm to about 15 or 20 degrees - at which point I got chilly and went inside. I can't remember if I was zipped into the bag or using it quilt-style, with the edges tucked in pretty good.