When you look in the mirror next, take stock, then breathe in deeply and straighten out your spine as if it continued up and out of your head and was being pulled from above. Use your back and abdominal muscles to support your spine, which will help your twins to stand as proud as they're able. Posture really counts!
Now, I know lots of lactation consultants are anti-underwire, but I used to wear them all the time and had no issues. Lots of bra companies even have mock underwire these days, which is like a flexible plastic version. Our own Belly Materna bra uses a flat, flexible version that shouldn't cause any mastitis problems. The real danger to nursing breasts is an ill-fitting (too tight) bra -- and lots of us just use the size we were pre-baby as our forever size. The next time you get a minute sans baby, go to a real lingerie store (NOT Victoria's Secret) and get measured properly for a bra. Don't just get the size you've always gotten. Try on a variety of styles, including underwire. You'll be amazed at the difference. And don't worry about how you look naked. Men are just happy to see any boobies at all, usually! :-)