Honestly, as a person who worked for years on standing jobs, fuck that. It wrecked my back and knees and I worked extremely hard to move to an office job. Now, decades later, my knees still creak and pop when I move, but I see people moving their desks to standing desks.
People, just go to a gym regularly and work out. There's no easy fix.
When I was a student I worked for 6 month as security guard on events.
Mostly the job was being standing at an entrance for 12 hours in a row (with a 20 Minutes break to eat), waiting for the 12 hours to be over (it was not the entrance for public so basically there were people crossing in the early morning and at the end of the day)
So I partially understand what you've been through. I'm lucky it was just a student job for me, but 25 years later it's still a bad memory.
People, just go to a gym regularly and work out. There's no easy fix.