That's not good Leggz.

The tailbone (coccynx) is one of the many bones that I've broken, and I remember how much it hurt to sit on.

I bought myself a circular cushion with a hole in the middle ...... Ahhhh! Instant bliss!

The one I got was a rubber blow-up one, but I see they sell foam ones now. They would probably work just as well, for less cost.