Your “comfort” book
I’m not sure I really have a “comfort” book these days. When I’m stressed, I often go back to books I’ve read and loved before, like one of the Discworld books, or I’ll read a new-to-me mystery or fantasy novel. It’s more a genre thing than a specific book thing.
Things I want from a book when I’m stressed and want to feel better: humor, suspense (without killing off people I like), and a straightforward-enough plot and writing style (or to have previously read the book) so that I can get lost in the book without having to stop and think too hard. I love reading slow, interesting books (like Jonathan Strange & Mr. Norrell or Lord of the Rings), but not when I’m depressed/stressed/whatever. When I reach for something to read to make me feel better, it’s gotta be exciting.