I highly recommend "The Maker of Dune", if you can find a copy of the book somewhere. https://www.amazon.com/Maker-Dune-Insights-Science-Fiction/d...

"The Maker of Dune" adds a lot of personal insight to his work. https://www.amazon.com/Maker-Dune-Insights-Science-Fiction/d...

I used to have a copy but sold it at some point. Apparently it's hard to find now, given the very high price.

Update: The entire book is in the Internet Archive! https://archive.org/details/the-maker-of-dune-insights-of-a-...