For a while I was knitting in a $10 'office' chair from Walmart. Had wheels, a small pad for the back, and no arm rests. I was very mobile and I had it for so long that the chair and my body comfortably conformed to each other, but, it was so old the seat cushion was worn away to the point where I could feel the screws that held the chair together poking me when I sat down. Not pleasant.
I recently bought a better office chair from Sam's Club... or maybe CostCo... but, it's a lot more cushion-y and it has arm rests which used to get in the way, but, now I just rest my elbows on them and knit. The whole chair also reclines (didn't know this at first, and screamed when I leaned back feeling like I was gonna fall
) which is also quite comfortable.
I spend most of my @ home knitting time in front of my computer. I've tried knitting in bed but that just makes me sleepy.