Sleeping in a hammock, at least for some catch-up naps, tends to reduce the pressure at any one point on my back

In a bed, sleep apnea is my worst enemy, and absolute worst when sleeping on my back. A T-shirt with a tennis ball or pool noodle sewn into the spine area might help you sleep more on your side, in case that relieves pain on other parts of your back. When sleeping on your side, a thin pillow between the knees may reduce pain in the lower back.

Another aspect to consider is whether the pain (in bed) is actually at the tailbone itself, or in muscles and disc tissue nearby. A topical anti-inflammatory cream like Voltaren might be useful.