Here’s the VERY BEST article on how to achieve and maintain a permanently unhunched back:
The background is this: it’s not your feet, it’s your toes and the direction in which they apply force (forward or backward).
We all start out with normal posture, supported by a normal and robust heel-and-toe stride. Somewhere along the way, our system (or PD demon, perhaps) switches us to a toe-and-heel flat posture with curved back, perhaps to keep you “safer” by discouraging big steps. Change your step and save your back! For real!
I got myself referred to a physical therapist who looked at my gait and said I had to step forward further to fix it — but that was 180 degrees wrong. When I showed her the right way she was shocked but conceded. I ended my engagement with her on the spot. Don’t be discouraged, but don’t think the PT advice you get is automatically right.