Agatha Christie, for some reason. My mom and I used to watch Mrs. Marple and Poirot on public television so there's perhaps nostalgia involved, but, she was a great writer. A lot of her work is now in the public domain and there are Standard Ebook versions of them, making them an easy pick if you like mysteries or are willing to give mysteries a try:

https://standardebooks.org/ebooks/agatha-christie

For the near future, I've got some of Emily St. John Mandel's books loaded up (I liked the Station Eleven series a lot), as well as Peter Heller's The River.