Check out 'middle grade' novels meant for 8-12 year olds. Don't let the category fool you. Books like 'The Graveyard Book', 'Wonder', or 'Percy Jackson' are masterclasses in tight plotting, heart, and clear themes. They're devoid of cynicism and are often profoundly moving.
They're also usually quick reads, giving you that sweet, sweet accomplishment hit of finishing a book in a day or two. That confidence boost is huge. They remind you of the unadulterated joy and wonder that made you love stories as a kid, before reading became an assignment or a chore. Reconnecting with that feeling is priceless.