I think your question should be, "should I be sitting so long?" There's ample evidence that extended sitting, especially relative to the amount of standing and walking, is detrimental to health (especially including weight). I spent years on the popular Herman Miller Aeron chairs, but eventually I developed lower back problems in my early 30s! So when I left my job and started working from home, I tried the standing…
Moving is better, all the way around. I'm biased I admit... but I think a walking treadmill (like the ones that LifeSpan Fitness makes) is the best all the way around.