I've been trying to find a new chair that is height adjustable and doesn't swivel, so that I can use it with my rudder pedals.
I've been using a dining chair for a few years and it's not very comfortable. Today I found this.
Nice little project for this weekend.
http://www.rogerdodger.net/videos/rudder_staythere.html
It might not completely stop the swiveling but it's much better solution than the dining chair.