Buy a bar stool - great to lean against and have other uses when not playing guitar. 8) 8)
:)
Coincidentally I was looking at one in the local guitar shop this afternoon. It was the nearest stool they could find to a 'guitar stool' - if there is such a thing. Fairly ugly unfortunately.
I did see another likely candidate in an office furniture store though. It looked a bit like a bar stool, but it had quite a pronounced circular 'step' all round it. Apparently it was a drafting stool - the sort of thing you'd sit on when working at a high draftsman's table I suppose.
So far the 'office chairs' I've already got seem OK , now I've modified them by removing the arms, raising the seats as high as they go, and getting the back rests at the right spot.