Tell us what you are interested in, and what other books you like. Nonfiction books are easier than fiction, so I would suggest looking for a nonfiction book on a topic that really interests you.
There is a big problem for learners. The style of written English changed during 1920-40 and became much simpler. Fiction written before then is written in difficult English, with long sentences, complicated grammar, and a wider vocabulary. Therefore, many "classics" (Charles Dickens, Jane Austen, Emily Brontë, etc.) are not good for beginners. Unfortunately, most books published after 1923 are still under copyright, and you must pay money to buy them.
I have one specific suggestion. "Black Beauty: The Autobiography of a Horse," by Anna Sewell, is in fairly easy English and quite interesting. It is often suggested for children because it is not in difficult English and doesn't deal with love or other "adult" themes, but it was not written for children.