Glad to hear that your cat is adapting to his new situation - I would, first of all, have your vet check for a UTI - I have a disabled dog who is 8, and from time to time she gets a UTI and will have accidents on her bedding and the carpet. We put her on antibiotics and it clears up and she can control her bladder again. If it is not a UTI, you can try what a friend of mine did once with her kitty: she got some infant onesies, cut a hole out the back for her kitty’s tail and lined them with pet diapers. At first the cat did not like them, but after awhile he actually enjoyed wearing his “clothes” and adapted to the diapers just fine. He lived to a ripe old age (18) and was very loved. He would actually let her know when he needed a diaper change! Purring can be either content or uncomfortable signs. Our oldest kitty Majic died this past year - we tore the house apart looking for her and found her lying on a towel in the bottom of a never used closet. She was cool to the touch and when we picked her up she was purring. We rushed her to our vet, but by the time we got there, she was almost gone. We got to say our goodbyes and she purred to the last breath. I wish you lots of hugs and love for your big kitty whatever comes, he is a lucky kitty to be loved so much for so many years!!
“No Bird Soars Too High If He Soars With His Own Wings” ~ William Blake