books for young readers
Swallows and Amazons, a long series, along with many other boating books (Stowaway by Karen Hesse and Carry on, Mr. Bowditch by Jean Lee Lathan come to mind) were enjoyed by my eldest, but are probably still too high a reading level.
The Swallows and Amazons stuff is also about indepence. My Side of the Mountain goes hand in hand with that. The Rosemary Sutcliff books about ancient Romans (The Lantern Bearers, The Eagle of the Ninth, etc) have a bit of that, too, but also get into the historical fiction that boy liked.
Some of the Edith Nesbit books, like The Magic City and Half Magic might work. Those are out of copyright so you can find and print a chapter to decide if you like them.
There's some Philip Pullman stuff that's easier to read than the His Dark Materials series (The Golden Compass, et. al.), things like Clockwork. The story structure of Clockwork is itself interesting. Sort-of a "Don't sell your soul to the machine because the machine will cash that chip in."