dear slutz,
i was in the same situation a few month ago and it took a long term to find the right stuff. in the end ther was 2 products:
-flaxfibre, smells a litle like straw, density is 30kg m3
-cellulose, its more dusty, but no prob with good fabric 70kg m3
i choose the cellulose slap, because of the very good tecnical specs.
product site is here, the stuff is called FlexCL:
http://www.homatherm.com
all the natural materials use borax for fire-prevention its toxic, but only when inhale the dust. you have to wear a mask. but its not outgasing anything formaldehyd like rockwool ore glassfibre. when its packed in fabric its all fine. there is a test in german magazine ökotest and it seems that everything is best with this stuff.
the performance is great, looks like it hase the same specs like this 703. 70kg mass on one m3 makes it very fine to build a vocalbooth i did. you can see the absorber i build in this thread:
my insprirations for DIY basstrap builders