When I think of novels about cats, Shirley Rousseau Murphy comes to mind. When I grew tired of reading children's and YA novels in my youth, my mom suggested I read the first book of her favorite series, Cat on the Edge. It would be the first time I ever read a murder mystery, and given it features talking cats, I instantly took to it. There's about 20 books in her series now and I don't know if she has any plans to stop. I would later read another novel of hers, The Catswold Portal, about a woman named Melissa who discovers she can turn into a cat (Based on Welsh folk lore if I am not mistaken).
An excerpt from her 'about' page on her website: