tml524,
In addition to opinions expressed here, you need the in-person evaluation of experienced board-certified plastic surgeons.
In theory, if you add an implant you will increase your breast size. In theory, you could have partial removal of natural breast tissue and placement of an implant of equal volume, and maintain your size.
I think you should be aware that breasts as large as double-D almost always develop sagging over time and with pregnancies, breast feeding, and weight loss. In order to maintain a lifted appearance, you will probably need future procedures. If you do not have a lift (mastopexy) at this time, you are likely to need one later. In my experience, you are probably going to consider decreasing your size in the future (breast reduction). Discuss all these issues with your surgeon, so that long-term planning can be done.
