Thanks for playing! Glad you got some enjoyment out of it, a minimap sounds like a great idea, I was worried the world was a bit too big so good to see your feedback mirrors that intuition.
SPOILERS:
Book #1 is the one under the water on the right, you need to drain that body of water to get to it.
Book #2 you need to go all the way around on the left, switch the current and jump into it then follow the path.
Book #3 is in the top right but the puzzle is a bit broken haha so I think it's easy to soft lock or cheese it.