Welcome to MR, Trilby
I don't have a Kindle, but I found a couple of classic Agatha Christie "cozy" mysteries on MR. I believe the download format is the mobi/prc for the Kindle?
If so, below are the links to them.
Christie, Agatha: The Secret Adversary by MR member Madam Broshkina
Christie, Agatha: The Mysterious Affair at Styles by MR member JSWolf