@Artemisia, I also love in print books being very old school. Even Kindle is difficult for me to use especially depending on the device.
I do not work with Hekate though, so I don’t have any recommendations for any specific books or authors. I follow a more Irish Pagan path & work with Brighid & the Morrigan, but also others with the Tuatha de Danaan with Brighid & the Morrigan when called for it. So, while do deep dives on other deities, I don’t follow or work with them enough to have any real recommendations.
Thank you for thinking of me though! 
it is very appreciated. Any prior information that I have used in learning about her before more recently is in this post: Hecate History, Theology, Mythology & the sources I used are in the post there too. 