@Reluctant_Sir
Not sure what you are using but if you have MS Word, saving it as .htm works like a charm, preserving all text modifications (Bolt, Italic, Underline, even super and subscript notation) as well as line breaks, added lines.
I haven't found any aberrations in the way my stories post since I started using that format.
As I mentioned, it not only handles all the various publishing marks (curly quotes, em-dashes and ellipses), but I've also included several foreign languages (using UTF-8).
The key is, though, not to use in-line formatting (except for the occasional italic), but to use Style Definitions, so the formatting is consistent and can be transferred (say to an ebook).