We use The Well-Trained Mind as a guide and use some Charlotte Mason style approaches to how I teach....if that makes any sense. LOL!
You'll find a ton of great information and free curriculum at
Ambleside Online.
I love their artist and composer studies, and refer to the booklists some as well.
I have enjoyed The Handbook of Nature Study - not a Charlotte Mason book, but it works nicely with nature studies. This
website has some great resources for nature journaling, studies, etc...
Good luck!!