Welcome @olliviv, It sounds like you already have a head start and a great mindset for dealing with PMR. I think physical activity along with healthy eating habits of the right kind of foods that help with inflammation is one of the best things we can do to help our bodies deal with PMR. I would hate to do it without prednisone but it does help to taper off as soon as your body allows it. Both occurrences of my PMR were started with 20mgs of prednisone. It took me 3 and half years to taper off the first time but that was before I made some lifestyle changes which helped the second time around and allowed me to taper off in a year and half.

You might find this site helpful.
-- Diet and Supplements for Polymyalgia Rheumatica (PMR):
https://www.arthritis-health.com/blog/diet-and-supplements-polymyalgia-rheumatica-pmr
There are a lot of other conditions that mimic PMR which may be why you've had a long and frustrating path to get your diagnosis of PMR. Here's more information on the topic along with a list of questions you can ask your doctor if needed.
-- Diseases that mimic polymyalgia rheumatica (PMR):
https://www.medicalnewstoday.com/articles/diseases-that-mimic-polymyalgia-rheumatica
Are you totally off of prednisone now and taking only celebrex and still having shoulder pain?