OUCH! Sorry to hear that, OP.
Definitely get yourself a coccyx cushion.
It differs from a donut cushion because the hole is placed directly in-line with the tailbone rather than, well, you know. There's a remarkable lot of sensitive tissue around the tailbone (as I'm sure you're now aware) and much like how a padded bicycle saddle puts pressure on sensitive bits between the legs, a normal padded chair puts needless pressure around the tailbone and can easily exacerbate tailbone injuries.