I use LibreOffice. Have you tried just making your index objects Heading1 style? Just make your normal Heading1 style at 14 pt. Seems to work okay, though I write straight fiction, not like nonfiction, more formal books, if that makes any sense
If you've gotta, nuke it. Save it as .doc when you paste it back into your editor. It's kind of a hassle, but when you switch from like Word, to OO, to LO, and to whatever else, you end up having a bunch of garbage hanging on.