Linus you should try an adjustable standing desk with a mid range chair. I'm a computer programmer so I spend ~8 hours a day in chair. When I come home I use a standing desk for additional programming and it's a great change. I do still sit for watching a movie and for some computer games. Sitting all the time, is not great for you, but standing all the time, doesn't work for all kinds of computer use and can be difficult if you're not used to it. Having an adjustable desk and switching presets throughout the day gets you moving and you will find you're even more efficient.
If you want to try out a standing desk without committing to the adjustable right away try this $22 IKEA hack http://iamnotaprogrammer.com/Ikea-Standing-desk-for-22-dollars.html
(Or if you need extra space this guy tweaked it and it ended up at $31 http://www.theimaginaryzebra.com/my-diy-standing-desk-the-2231-ikea-hack/)
You can have the best chair in the world, but you'll still be sitting!