See the first sentence of my other reply. I made an assumption, apparently not warranted. Chapter Numbering requires the use of the built-in heading styles. These can be configured to look like yours current text.
Why use Microsoft Word’s built-in heading styles? by Shauna Kelly

You might be able to get a cross-reference to a bookmark, but I'm not sure how you could put the chapter number in a bookmark. It certainly would be a lot harder.