I also severely overpronate although I have high arches and stiff feet. I've read about going barefoot or using barefoot shoes and I'm intrigued. What I am certain will help both of us, though, is foot exercises: picking up marbles & pencils, rising onto balls of feet and using resistance bands to exercise the muscles attached to the posterior tibial tendon. There's some info here: Posterior tibial tendonitis exercises
Take good care of your hips too- iliopsoas and general alignment.