What are you using it for?

I'm considering using it for a set of professional, personalized stationery.

But what is the sans/serif opposition trying to convey?

So, you could stick to something more "modern" like Proxima Nova or Gotham for a lower level of opposition. Or you could pick something like John Sans, which will contrast in two ways, both in serifs and stress, or you could go all the way and pick a humanist sans like Optima or Candara.

Good question...I didn't really explain myself well. The sans serif will be used on a resume and I want to use Didot for headings and sub-headings because I love the elegant feel of it. But for the smaller type-the meat of the resume-I want something more legible at small sizes.

Alright Sans would be a nice choice for something a bit more modern, while still having personality.

penn

Helvetica, which is Didot with the stroke contrast reduced.

Helvetica, Akzidenz Grotesk, anything in that range. As John already said - same pen construction, which is pretty good base to build your pairing upon, also consider x-height in consideration when pairing it directly.
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Sandro