I've seen a lot of mayo recipes call for Olive Oil, or whatever oil is all the "healthy" food craze rage at that moment. Personally, I recommend the most neutral flavored oil you would otherwise use in cooking. Mayo is a supporting player, I don't want mine so strongly flavored that it doesn't...
a pinch of white pepper. and homemade mayo, since we have all those fresh eggs anyways.
Honestly, I'm not a fan, particularly of the mustard-heavy varieties. Mustard is normally added as an emulsifier. If there's enough to serve that purpose, there's enough in the recipe. My view anyways...