I like the Freedom chair from Humanscale. http://www.humanscale.com/products/freedom_index.cfm?detail=features
You're referring to a "Balans" chair. They're terrible. The fixed leg position would be a favorite device of Torquemada. Via's Swopper: http://cgi.ebay.com/Irresistible-SW...ryZ20496QQssPageNameZWDVWQQrdZ1QQcmdZViewItem I have a few as bar stools, very comfortable.
I'll be standing when i can justify spending 6k to the wifey on an electric, dual-tier, adjustable height table. http://www.afcindustries.com/corner_DT_side_mahagony.htm The adjustable height gives you the option of sitting or standing. Sitting on my butt 10hrs a day can be brutal on the rear. Iâve added extra padding to my office chair using a cushion off a wing chair in our formal living to save my butt till I get one of the above tables.
I have gone through 3 chairs myself, but I'm always at the computer. I would really say that you should invest in a good chair. I've used some pretty crappy chairs and I noticed I wasn't feeling comfortable by the end of the day. I'm 19 btw, so I can't imagine how it would feel if I was older. So buy a good quality chair, and be sure to get some exercise too