Find your niche.
I'm lying on my bed upside-down (my head is where my feet are supposed to be when sleeping) with my back facing up and my feet crossed. My elbows prop my upper body up so I can use the keyboard and the laptop touchpad in front of me. Also, my laptop's on a chair without a back, opposite the bed's headboard, and it's positioned within arms reach. I don't usually use my laptop while lying down, and when I don't I sit in a typical position (my back tends to hunch, though), but I'm lying down right now because it's more convenient. :D And it's night time here, too, so it's a bit more comfortable to be in a position that I can doze off quickly.