I've seen one suggestion on how to do this directly from an Excel file, but
frankly, I wouldn't bother.

I suggest that you try the following:
a. Select/Copy/paste your Excel sheet into a Word document, choosing a
format that retains the formatting you want. I think one of the options that
ends up as a table will do.
b. use the Word document as the data source, but instead of using
MERGEFIELD fields to insert the data, use { REF } fields. In fact, you may
have to go slightly further than that, e.g. if you have a field named
"myname", you may need to use

{ myname }

rather than

{ REF myname }

If so, you need to avoid using fuield names that clash with standard Word
field type names such as REF, MERGEFIELD, FILENAME, SUBJECT etc.

If that works, but you need the process to be simpler than that for end
users, as far as I can tell it should be possible to write a macro to do it
but I don't have any code for that myself.

Peter Jamieson