My game-bunker (office) is great! My computer chair is wonderful and very comfortable. It's a big pleather officer manager type chair that rolls. I also have a firm but nice pillow to help my posture while I sit. I don't actually use a real desk either. I use a large kitchen table, and that leaves so much room for snack, beverage,bobble-heads, pens, notepads, etc. I also have an adjoining kitchen table right next to me (it forms an 'L' shape) that holds my printer, laptop (with wireless mouse and speakers), and record player. I also have room for a small stand in here, and I am soon going to find a small t.v. and bring one of my consoles in here as well.
I love my PC gaming life-style and game-bunker, even though I do have consoles. And when I play consoles, I just push the couch closer to the t.v, and sit (with my pillow!). I don't usually lay down and play games, on my stomach or back. I find the way the arms are positioned very uncomfortable (especially at the elbow). Unless I am in bed sick, and have my laptop and wireless mouse for company, but even then I use all the pillows to prop myself up, and technically, I am still sitting.
Either way, I think sitting is just as comfortable (but perhaps that's because I've been PC gaming for quite some time). If I lay down and play games, I feel like a lazy slug.