My guess is this problem is not to do with sitting per se; it's how your (partly unconscious) attention is distributed. It's not just work/gaming/movie that requires bandwidth, the body needs some too. If you can't walk about then better posture and even little things like wiggling your toes might be helpful.
Improving physical health is a goal of some types of meditation. It's hard to generalize about meditation in a useful way, because the term covers such a wide range of traditions. It's a bit like trying to generalize about religion (not coincidentally).
Different type of sitting. I would guess the cross-legged, straight-back position is great for your core, as well as improving hip and knee flexibility.
Yes, if you are meditating. However not if you are, say, programming and drinking coffee. The use of the mind while sitting is typically ignored in these studies, I think because it's hard to measure and thus considered subjective and non-scientific (despite being relevant here).
http://images.huffingtonpost.com/2014-11-19-ChairSittingGood...
My guess is this problem is not to do with sitting per se; it's how your (partly unconscious) attention is distributed. It's not just work/gaming/movie that requires bandwidth, the body needs some too. If you can't walk about then better posture and even little things like wiggling your toes might be helpful.