I'm a hefty boi, and used to carry large, heavy items, walking an average of over six miles a day on concrete, as well as spending a lot of time walking up and down metal stairs (often with a load). I got plantar fasciitis pretty horribly.
PT didn't do me any good...in fact I feel it exacerbated the situation (and I'm a great believer in good PT). I got custom orthotics cast, which cost in excess of $300 17 years ago. No dice. Wearing a "boot" on the worse side for six months did nothing. I suffered for over three years and visited several different doctors and specialists.
What finally worked for me was getting a pair of Lowa Zephyr GTX boots (they make low which look like sneakers, mid, and high models) and a pair of Dr. Scholl's inserts from Wally World, the ones where you stand on a machine in your socks and it measures your arch height and how you carry your weight. I also started wearing Fits socks. The boots were expensive, but lasted longer than any others I've bought (including some well-known and -respected leather work boots). The inserts aren't cheap, but after they wear out, rechecking on the machine may show changes in which insert is needed due to changes in foot shape or body weight, so I always have the right set. The socks are spendy compared to Hanes or Fruit of the Loom, but they wear like iron, my feet never stink or feel sweaty, and having them on feels better than going barefoot.