I don't know what kind of cornbread mix you are using but sour cream should make the cornbread lighter.
I make mine from scratch. Whenever I bake with sour cream, yogurt or buttermilk, I add a little baking soda (1/2 teaspoon). But, with a mix I think you'll be okay because they seem to have more leavening. I can always taste it in Bisquick and Jiffy corn muffin mix. That's why I don't use it.


