Jon, Flora, and the Odd-eyed Cat might be hard to find, but if you can get a copy, I'd recommend it. It might even work for mature eleven or twelve year olds, but I was kind of confused with the magical realism when I read it at that age, so I feel like it's slightly better for teens.
https://www.goodreads.com/book/show...?from_new_nav=true&ac=1&from_search=true

Happiness can be found even in the darkest of times, if only one remembers to turn on the light.