When our dogs were puppies, we went through a few dog beds because they would chew and make holes in the outer cover and the stuffing would all come out. Unfortunately, there’s no guarantee a dog won’t destroy a brand new bed.
It would be better to buy a cheap one if your dog is young or if you don’t know what your new adopted mutt might do to it.
In our house, we have three kinds of beds, besides the old mattress.
The round one, I bought at Costco and it’s the Chocolate Lab’s favorite. He fits perfectly on it especially when he curls up in a little ball.
The one with sides is the Beagle’s bed and was bought at a local pet store. All 3 dogs have been using it, even the big dogs, who barely fit on it.
The rectangle one is an older model I bought at a pet store also, it’s not being used much though.