Do I need a lower jaw surgery or a double jaw surgery? (photo)

I would like a jaw surgery done to correct an underbite and protruding lower jaw. I have a long mid face too which may be corrected with jaw surgery. I am not sure if the long face is due to a long mid face or a long jaw? I would definitely need to do my lower jaw. Do I need to do my upper jaw as well? Can you explain to me why and what are the benefits to do the upper jaw? The OM surgeon I saw seems to be a conservative one and she said I only need a lower jaw surgery.