After putting up with a step stool as my observing chair for the first few months after re-entering the world of astronomy I decided that I needed something more height adjustable and portable. It always seemed that neither of the two steps was ever at the right height to make for comfortable observing and it always seemed that the stool was more of hindrance, overall.
There are loads of designs on the net for building your own observing chair and lots of suppliers that will sell you one but most of them either were designed such that they would be difficult to fit into my Mini Cooper or cost more than I was willing to pay. With a few I even had concerns about the chair portion staying where it was put.
Then I ran across the Home Built Astronomy Projects website and an observing stool design by Rod Nabholz at http://www.homebuiltastronomy.com/stool/ that looked like it would work perfectly.