for tent camping on a mattress my wife and I always use a double sleeping bag liner and zip our fleece bags together over that, the great part about it is that you can't end up sliding out of the bed, and there are no blankets in the way for playtime.
However the sides to the bag are a real pain to use in the tear, in the tent we have to slide around and crawl out of the tent anyway. The big plus of a properly built tear is the ease of getting in and out, you shift your weight to the inside of the tear, and pivot your feet out the door, no sliding, scooting, crunches or crouching. this only works with a regular sheet set up on a bed. fitted on the bottom, flat on the top. Since you are in a tear, you can't slide off the mattress. (no matter what you are doing