Preggers by Therafirm now makes an amazing maternity support belly band in several sizes and colors! They are seamless and super stretchy. They expand for the various stages of pregnancy, while also providing support. Wearing the maternity support belly band can help ease back pain and make you feel more "put together". Under clothing it will make everything fit better and feel more comfortable. Can also be worn post pregnancy when abdominal support is still needed.
As a note, the support band is not intended to hold clothing in place. It is to provide compression support to your growing belly. Compression products for pregnancy are such a great investment!