Look for any pet bed.. dog, cat.... whatever. But it may be trial and error to see what type they may decide to chew. If they get to the stuffing, you'll need to replace it so they don't ingest any part of it.
Here's one of many beds we had over the years. It was made for dogs and had a very tough, thick fabric. They managed to chew it anyway.
They are all different which type they will like too - mine won’t sleep in anything with sides so she has a flat dog bed to stretch out on (even if she usually chooses to sleep on the floor next to it instead)