I've made a few smoking caps, and love the style of hat. It's simple, but can be embellished with embroidery or applique or other techniques. And - oh! - the tassels! Kathleen M. O'Brien of Vintage Fashion Explained has put together a book on them.
(Full disclosure: Kathleen is a friend and gave me a copy in return for my technical assistance with the book. A review was not requested or expected.)
I've seen some of the smoking caps pictured in the book in person, and they're lovely. The book includes photographs and technical details on several caps in her collection. If you're reading them on a Kindle, you can zoom in on the caps and see the detail. (The zoom feature doesn't work on the Kindle app for my computer, but that's an issue with the app and not the book.)
If you're interested in making your own smoking caps or if you have an interest in Victorian embroidery and embellishment techniques, you'll find a section on construction along with patterns from period publications, along with definitions of terms used.
Kathleen is working on other books, and if they're as detailed and well-researched as this one, they should be good.