[exaltedwombat]

To be even less Sigil-centric:

(I expect this thread will be moved to a more appropriate forum soon. But have your answer anyway. We're here to help.)

Use Calibre to convert your EPUB to DOCX. One click. Done. (Not the complicated method suggested in the link you quoted in the second message in this thread.)

Now you can (and should) adjust your thinking to a page-based world. You DO now have absolute control over where pages break, where lines end. Your Table of Contents and Index can now use page number references rather than hyperlinks.

And there's the practical stuff. Bleeds for the cover image. Gutters - the extra margin required on the right hand side of even-numbered pages, the left of odd-numbered ones to accommodate the binding. The whole 'look' of the book - printed books tend to make much more use of white space than is appropriate in an eBook.

Much of these issues can be bypassed by using a template. But if you prefer to keep full control and submit a final PDF version (easily exported from Word) don't panic! The process leads you through a whole system of online proofing where problems will be detected and reported for your correction.