I gotta second KB's suggestion of "Earth Abides". Especially after seeing that "The Martian" was a favorite for your group. While very different stories, the core is similar: you are deeply living inside the story, from the narrator's perspective, and the narrator is trying to process and understand what is happening around them and how to deal with these events. Earth Abides is not exciting. And that's part of the beauty of it, and why it has stuck with me... the story lives and continues long after you have read it. The pace of the book is the pace of the seasons and the years. You FEEL the passage of time, but it doesn't get boring or need a big action scene to keep you interested. I read the book for the first time several years ago, and I honestly think about it most days.