When Bearcat, my 14 1/2 year old Maine Coon died, I threw away everything that belonged to him. Not from sentimentality but to protect any future cat. When I adopted Bear, he was unknowingly exposed to feline herpes, which my other cat, Dali, had but had not presented symptoms of as yet. As soon as we found out about her illness, we started both cats on daily lysine that helps prevent outbreaks (there is no cure); for Dali it was too late -- she had been born to an infected mother. But it kept Bear healthy for many years. He died from kidney failure and cancer. Before bringing home a new cat, we threw all his stuff away and disinfected everything, so the herpes will not be passed on.
I asked our new kitten's breeder if her cats were used to cat beds. They tend to ignore them but love little cubbyholes or cubes they can hide in. Which fits what I've seen of Maru, a Scottish Fold popular on YouTube for diving into boxes and other small spaces.
Years ago, I made a bulky-knit bathmat out of Sugar and Cream yarn. We had no need for it here in our new home, so I unraveled the mat and am using the yarn to crochet a cat cave. I found the pattern online, made of t-shirt yarn, but holding 3 or 4 strands of cotton yarn together seems to make a firm enough structure. . . . . My hands got tired so I took a break and sketched my work so far.