Dear Tom,
I'm not sure if this book contains any information about Heinrich Baum (I leafed through it only once, quite a long time ago), but it's quite detailed and gives quite a lot of information about JG 27:
https://www.amazon.de/Jagdgeschwader.../dp/3879432155
On Amazon.de, there is also this book:
https://www.amazon.de/Chronik-Jagdge...13034611&psc=1, but I'm not sure if it's different or if it's a different edition of the same book.
Good luck!
Best regards,
Teresa