Hi! I think Gurney's along with Loomis' books are great resources and will provide a solid foundation. I'd also add Alla Prima II for both painting and the fundamentals as a whole. For more specific topics, the books I've personally found to be most helpful are: Composition - Framed Ink by Marcos Mateu-Mestre; Picture This by Molly Bang Figure Drawing - FORCE: Dynamic Life Drawing by Mike Mattesi; Figure Drawing - Design and Invention by Michael Hampton; Drawn to Life by Walt Stanchfield (this is more geared toward animators but still has a lot of valuable lessons!) Drawing Fundamentals - Classical Drawing Atelier by Juliette Aristides I hope this helps! Best wishes for your artistic journey :)

I know I'm late to this, but I really like Andrew Loomis's books. I bet maybe you've already heard of him--your drawings remind me a little of some of the things I've learned from his books. Several are available for free on the Internet Archive, if you can access this resource. Creative Illustration is my favorite! I checked out your page and I love your drawings! Keep up the great work!