Retrocalcaneal bursitis issues

Hello,
I sought out sports medicine treatment for heel pain. I was diagnosed with retrocalcaneal bursitis and received a cortisone shot and wore an air cast for a couple weeks. When I tried to get back into my walking routine, the pain persisted. I was referred to podiatry.

I was advised to wear orthotic insoles presumably suited for heel pain and to stretch. Wall calf stretch and lower calf stretch. Not helping. I can barely stretch without severe pain. I have found myself adopting a flat footed footstep more like slapping because of the tightness. The air cast provides some relief, but I don't want to depend on that.

Are there more specific stretches I can do? This really limits my capabilities and I want to resume walking because I like it for exercise. Not a fan of biking or swimming. Is minimal footwear a better option to encourage foot flexibility? Are expensive supportive athletic shoes more harmful than beneficial? Any advice you have would be greatly appreciated.