If that’s the issue, I wonder if it would be worth having a larger pair of jeans taken in at the waist

Edit: I don’t l know if I’m curvy enough to weigh in, but I did always have problems with gapping in the back before I started to consistently wear the same leather belt. It has actually molded to my body. It is no longer a flat strip of leather. My pants feel like they fit much better, and I think it’s the result of finally getting a good quality belt that I’ve worn enough to break in.