I don't have any advice about your current mattress, but I have collected many links for organic mattresses. If you tell me what your price range is I will post all the links I have for mettresses in that range.
We bought our crib mattress from Dax Stores -- they have free shipping and it was the best price on the web for cotton/wool org crib mattress, so I'd assume their prices on adult-sizes would be comparable?
The crib mattress is gorgeous and very well made. I highly recommend.