He could of course buy the Atlantis word processor which outputs epub natively and then run titles through Sigil to add the table of contents.
Then you only need calibre to convert to mobi and you have an ePub ready for all the non amazon stores.
Microsoft Word has a Table of Contents feature as well. If one already has Word, there’s little reason to buy another word processor. Once the HTML is created and uploaded into Calirbre, Calibre will convert to any viable format.