I don't have a good source for green mattresses for 'ya but it seems Francesca's choice is a good one. I use simple upholstery foam for all my mattresses and don't have big concerns about disposal. In my area, all foam and mattresses go to a separate disposal chain that processes and reclaims the foam.
The video linked in one of the first posts has a lot of inaccuracies just as some of the following posts about solar arrays causing clear cutting and wind issues or wind power causing excessive bird death. I'd suggest that folks look at the facts and filter what they see and read. There are a lot of folks out there with an agenda that will push opinions as fact and, in some cases, are totally untrue.