There's a company doing one based on plasma treated sheep's wool that looks good (if a little pricey).
Their pitch is that unlike other sheep wool based insulation theirs doesn't have issues with insects moving in, I guess the high heat means it's not edible and absorb water any more.
EDIT: Isolena in Austria is the company.
They seem to be one of the only ones whose insulation is purely wool and doesn't have a bunch of recycled plastic in it as well.
Heritage House has an (opinionated) article:
https://www.heritage-house.org/stuff-about-old-buildings/ins...
Edit 2: It's Plasma treated not heat treated.