I bruised my tailbone back in the late 1970's as I completed the manual bicycle exercise that we used to do in exercise classes at the YMCA. Lying on your back on the hard floor with your legs in the air and your elbows on the ground with your hands supporting your back, you just cycle away with your legs. Well, when I was ready to stop cycling, I let my legs come down too fast and I hit the floor hard on my backside. The pain took a while to become evident, but after going to an Orthopaedic doctor who told me I had bruised my tailbone and that recovery would be slow. X-rays indicated that I had not broken the bone. The doctor gave me some anti-inflammatory medicine but that was only taking the edge off of the pain.
Back then, doctors were recommending that your totally change how and where you sit, each and every time you sit, no exceptions. And the embarrassing part was that I was to always sit on what we used to call the donut hole, a pillow used by patients with hemorrhoid problems. I got one for my office chair at work, one for use in my house and another for use in my car. I had to sit and get up very slowly each time and try to never sit on a hard surface. I had to plan my seating arrangements for everywhere I'd be going every day. When we went to the theater to see a play, all the chairs were hard wooden ones so I would have to sit on one side of my backside and cross the other leg over my knee. And as you mentioned, standing and going for a brief walk would give temporary relief.
This went on for 2 full years. I was diligent in following my regimen and it finally paid off. I wish I had been able to find the materials such as you have gathered. If it is not too old-fashion, I would recommend using such a pillow or something similar and be very conscious about sitting down slowly to prevent a setback.
Note from Jon Miles: Most sufferers find that a cut out cushion is much better than a donut cushion.