i have some soysilk for spinning, and yes, it's luxuriously soft. have you tried tencel/lyocell? it's made from cellulose (in a process that's apparently relatively green), and i've finally found a local source that resells the fibre. it's not as soft, but softer than hemp.

something else i'd like to try is ecospun/fortrel, which is made from recycled pop (PET) bottles -- not natural, but hey, at least 100% recycled -- but i haven't found it yet locally.