They make an inexpensive seat cushion with a little cut out for your tailbone. I have one to use in Peter's car ( it is a memory foam one). I also had one for travel that was self inflatable. I haven't used it for awhile, mainly because I have to take so much other stuff now, like knee braces.
Thanks, Gail. If I'm not healing towards the end of the month, I'll go get one.