Not sure about your shape or your pocketbook. New York & Company has good prices, and the selection is not overwhelming. Wherever you go (I prefer online, as well.), I would suggest that you find a simple dress, maybe a tent dress, something with no waistline but hits at the knees. (The dresses that cut in at the shoulders are flattering on me. That's the cut that sometimes requires a racer-back bra.) You probably don't want it to cling, but you should invest in Spanx or the Hanes things (Hanes is at Walgreens). The trick to dressing it up would be to wear some FABULOUS shoes (ornate, sparkling, detailed, boldly colored--whatever makes them fabulous), maybe with matching earrings. You can dress up your make-up, too.
I've been through recent body changes and have had to improvise for everyday and for special occasions. Where I shop online: New York & Company, Nordstrom, Macy's, Zappos, Bluefly.
Remember, also, that the key to looking great is feeling great. A confident woman can wear just about anything anywhere.