I'm a thrasher when I sleep - lots of movement, many different positions. Using a mummy bag as designed, and a thin foam pad, resulted in many nights of poor sleep in the backcountry.
About two years ago, I switched to a 2-inch-thick Therm-A-Rest pad – vastly improved comfort.
I was tempted to try a quilt, but couldn't justify the expense. So I started using my sleeping bag like a quilt. I just open up the zipper all the way, and drape it over me.
Much more comfortable, and just as warm into the upper 20s. Between the thicker pad and the sleeping-bag-as-quilt, I'm sleeping much better. My next major purchase will be a quilt, maybe the EE Enigma.
I'm also a pillow mangler - sometimes I want a thin pillow (on my back or stomach), sometimes I want a thick pillow (on my side). At home, I can reshape a feather pillow literally in my sleep.
Lightweight backpacking is a whole different story. If it's cold enough, I don't have extra clothes for a pillow, and water bottles & similar stuff doesn't mangle.
Just a couple of days ago I got a Big Sky inflatable pillow. Haven't tried it yet, but it looks promising. I can sleep on the skinny part in the middle, on one of the ends, or standing on a long edge.