Reading the previous posts, I can't help asking (and this may ultimately belong in another forum), if anyone has tried this one:
https://daisy.org/activities/software/wordtoepub/
It's Windows-only, uses Pandoc as its motor, and produces accessible epub3's from any properly formatted .docx - works as an MS Word plugin, or standalone.
I have tried it, and though I don't like its formatting of images, it might work for others. And it's probably better, not least for newbies, at producing epubs, than all those more or less esotheric procedures that have been invented over the years for lack of better.
Regards,
Kim