I do my writing in LibreOffice. Each chapter is built off a common style Text document (*.odt). The chapters are accumulated into a Master document (*.odm). The Book cover, Title page, etc. non-chapter preamble are in the Master doc. The Chapters and postamble stuff are Text document. The table of contents is hand rolled in the Master documents. The links are bookmarked to the Text document’s chapter title. The text of the title is a Property called Chapter. This lets me bang out chapters without having to bother much with the technical aspect of the layout, at least for producing a PDF product.
A couple of years back I had stumbled across a light recipe for making a 3D book from a book cover design in GIMP. I did this for the Drift cover. It was a struggle, as I remember. I thought the results worth it, to make a marketing statement.
Work has progressed far enough on the formatting of my titles I think to finally release my children to explore the world. It has been a journey of learning for me.