books on enneagram?

ive recently picked up typology again and decided to do a full readthrough of helen palmer's book on enneagram. my only problem is it was published in 1988 and though im enjoying the read, there are some minor details that show the book's age.

does anyone know of any similar books published more recently? im sure the vast majority of the content will be the same, but id still like to explore more options.

im mainly looking for in-depth explanations of the system as a whole + individual sections on the types, but im also open to books on the specific types (if those exist). any other reads relating to typology in general would be appreciated too!