Id like to try wool.
we have duck and goose feather down? Or similar, had it for years I bought it from a website I cant even remember now and its a winter one with a separate summer one and you can attach them both together with poppers to make a super warm huge duvet!
I do love it but for some reason with these feather ones, they make lots of crinkly noises when you move and sometimes I think wouldn't it be nice with a synthetic one or something which is silent! I think it's the price you pay for feathers ( I know im weird)