Hi, fellow tall apple mom! I wear a 12/14 too.
I have to agree with wrap dresses and dresses with "ruching" and gathers at the sides, like many that velvety chocolate found for you. But in my experience you really have to try them on. . . just this weekend I found what I expected to be a wonderful dress that did nothing for me, and a stretchier dress in a medium that I thought would just be tight in all the wrong places but ended up coming home with me!
I agree with Shannon. . . if you can post more details about the formality of the dress you need, you'll get a lot of help here! We've had several members even post photos of themselves wearing several options to make the best choice!