I was given an interesting book called 'Bookbinding, Limp Bindings from Tallin' by Monica Langwe Berg showing historical books and interpretations of their structures by binders working today in Estonia. So I've taken the historical structures as my starting point too and made some books of my own.
This is a small leather pocket book, no glue, only the stitching holds it together.
Another small pocket book with a leather cover.
I've been trying methods of binding that use only cloth, not stuck to boards, for the covers and this is a start. Cloth frays and is generally soft and flexible which means that many binding methods are not suitable or durable. This is a soft cover and could be used for informal manuscript books.