I've been using the cheap mattress/crate pad type beds in the crate, but he takes great delight in pulling the stuffing out! At the minute, he has an old beach towel and two ikea fleece blankets, which also have holes in them and just don't look very comfy.
I'm after some kind of crate liner, doesn't have to be thick, just comfy enough to lay on, and then I'm happy to chuck fleeces in there for him to burrow into.
Bizarrely, the chewing is only happening overnight, not when I'm out, and he's a very quiet, stealth chewer! I've tried leaving him loose in the house and he ate a chair :(