I was kicked in the coccyx when I was about 10. It hurt for a few years, but sitting down was fine, I don't know why. In January 2007 it started to hurt again. My GP and Gastroenterologist both said there was absolutely nothing that could be done, even when I asked them to refer me to anybody else who could help.
I waited until about June before I googled for coccyx cushions. I had a rubber ring but discovered later that there was such a thing as a coccyx cushion. I ordered one, saw coccyx.org and separately saw an ad, I think, for the Sayer clinics. I called up and asked to see someone about my coccyx and was told to see Dr. Durtnall (see Doctors and specialists in the UK). I was a bit nervous about this, as nobody in my family had ever been to one.
Dr. Durtnall saw that I had a bad posture problem (and looking in pictures from then, I now think: wow, I had awful posture. I had 'the nerd hunch' as I call it.) and told me how to correct it. He also gave me a heel lift in my left leg, as a standing x-ray showed that one leg was a fair amount longer than the other. My posture is about 90% better.
My coccyx injury wasn't simple (e.g. a quickly fixable dislocation, which I've seen some lucky people write about) as it was an old injury, so I was given exercises, and gluteus maximus/coccyx massages with a thumper, and over about 8-12 treatments my coccyx got about 50% better. It's still not 100% ok, but I moved from the UK to the USA a few months after I first saw Dr. Durtnall and I'm in the process of finding a decent chiropractor. It seems that the skills of chiropractors are highly variable, or at least: they may specialise in different things (to be nice).
I recommend Dr. Durtnall, as he's definitely been the best of three (so far) chiropractors I've gone to, and he specialises in coccyx injuries. He also wasn't afraid to tell me exactly what was wrong with me: "Duncan, lose some weight! and don't hunch up like that!". He also recommended that I not sit for long periods, and at the moment I'm in the process of getting a standing workstation, which will definitely be a big help. He also recommended a better chair for me, and advised me on sitting and standing posture, and gave me some exercises to loosen my tense butt-muscles.
I still use a cushion and I've just ordered a Tush Cush off Amazon, but haven't received it yet. Before that, for about 4 months I've been using an Argos cushion, although it seems the one I had has been discontinued, but I need a new one as the Argos one has become pretty flat.