if you are car camping, or sleeping in the backyard in an emergency, then any good sleeping bag from an outdoors store (or even K-Mart) should work. Just check the temp rating. If you expect to sleep at freezing temps, get one rated down to -10 degrees.

the issue of bulk and weight comes up if you are backpacking the gear. at that stage anything bulky is a huge hassle. I use a good goose down bag for those purposes. More expensive, but much better for reducing weight and bulk. Remember to keep your down bag very dry, or you will be an unhappy and cold camper :-)

Pete2