David–
Great to hear you are seeing improvements with this.
Next do it on the floor vs doing it on a mattress.
Here are a couple episodes that hit on sleeping positions which will help to continue to improve the situation.
Episode 39: Sleep, Pillows, and What Your Low Back Says About Your KB Swing
Adaptation Error: Don’t Sleep on Your Stomach & The Right Bed
This may hit some that will help improvement in that area as well.
Jill Miller Smashes Your Guts! (and psoas, and tacked down viscera, and matted down abdominals…) Part 2