American Securities or Liberty Safes are great! As others said depending on your space and location, you should buy a safe bigger than what you have. Also look at fire rating too.
So sorry to hear that OP. Our dog had a very similar situation, but was best to just have him live out his days. Hs quality of life did eventually degrade to to the point it was selfish to keep him going on so much pain. We took him to the vet after Thanksgiving and spent our last few moments...