[andrewl]

You could try this:

http://www.nadachair.com/

It feels good for my back, but everybody is different.

[irickt]

This looks like a good support ("an extra muscle"), but it's important to train your own muscles.

Rowing is great for strengthening the core and for stretching the back. I "row with Xeno" http://www.row2go.us/

"Belly button to the spine, chest up, shoulders down."