You can use any salad greens you prefer. I generally use an equal mixture of romaine lettuce (for crunch), spring mix, and baby spinach.
In any recipe that calls for mayonnaise, I usually use Canola oil mayo, which has half the calories of regular mayonnaise, but tastes better than "light" mayo. I used it in this recipe and it tasted great.
I always use light sour cream instead of regular, because I can't tell a big difference.
Keep this salad covered with foil while chilling, or if you have leftovers. The foil blocks odors better than plastic wrap and will prevent your refrigerator from smelling like onions.