Because we stood in front of the same decisions this year, I can only recommend to use wood not stone as building material. And wood fiber insulation. Building techniques in that area are pretty advanced. (At least I hope so, let's talk about it in twenty years again :D )
I think this has already been addressed by the sibling comment to my question. Insulation does not have to impermeable. Its purpose to prevent the loss of air carrying heat with it, not the transfer of moisture/humidity.