A few years ago, Osprey made removable belts that were contoured and could be heat molded to individual shapes. They can still be found in some of the shops.
I used to ragpick the shops for contoured belts with mesh on the inside, so that when a pack project came up, there would be good choices available.
Here's a pic of one of them on a prototype that didn't quite make the cut:
(Please excuse the clutter - too many projects going on at once.)
Can't remember where I picked this on up. But like it for the mesh on the inside, the contour shape, the horizontal seam that encourages the belt to contour over the hipbone crest, and the recessed middle that prevents anything from coming into direct contact with the base of the spinal cord.
Avid MYOGers may notice that the belt is upside down on the pack! When correctly installed, it would form a nice conical shape over the hips.