OakLeaf, I just got back from trigger point therapy. The therapist recommended using medical-grade felt as padding. I guess it's denser than foam and lasts longer. This web site http://eGeneralMedical.com has some in 1/16, 1/8, and 1/4 inch thickness, though you have to buy LOTS of it, so not cheap -- around $35. She gave me some to experiment with in my shoes...

Good luck!