Being somewhat granola heads ourselves my wife and I opted to get an organic latex mattress. It was equally as pricey, but it does have a 10 year warranty that does not depreciate.
www.organicmattressstore.com You can choose the firmness that you prefer and you can even have one half be firmer than the other.
We looked at the Select Comfort beds and I was turned off by their warranty because they pro-rate it for every year that you have the bed. I've also heard mixed reviews about their customer service when the warranty is needed. I know plenty of people that love them though.