For rainy days I don't go for just any book. I don't like books too summery because I actually like rainy days. In the summer I like reading about cooler areas of the world when it is super hot and humid. For rainy days I like to start a fantasy series, read thrillers, or darker novels. Here is a short list of some books I've read that you might like to try on a rainy day.
1. Harry Potter and Philosopher's Stone by J.K. Rowling. I like to start my series with a feeling of comfort that will help me feel nostalgia later.
2. Never Let Me Go by Kazuo Ishiguro. I like the pairing of the author's writing style and plot for a rainy day.
3. The Thirteenth Tale by Diane Setterfield. This one is eery and strange that centers around an old woman and her story.
4. The Girl on the Train by Paula Hawkins. A good thriller to get absorbed in with the rain to create a great ambiance.
5. This Is the Story of You by Beth Kephart. I am currently reading this and it was raining yesterday all day. I got lost in the story and recommend it.