Hope my reply isn't too late.

I'm sorry this seems long but please read it all, whoever you are.
I am 18, and have had this problem since I started developing. Honestly, I am very unhappy. However, I will work on firming my chest muscles, or just trying to be happy with myself before resorting to surgery. You see, your breasts often look saggy only when you are not wearing a bra, and tend to bother people the most when they have no clothes on... If you have no clothes on, however, a surgery would still make you self conscious. You could wear bikinis just fine, but underneath, you will have nasty scars. The scars don't go away, though I hear after a few years they may lighten. I would rather not go braless under my shirt than to have scars and wear tube top.... Your breasts will sag again one day, and there goes your money. It's a part of nature, unfortunately. Nature always gets the last laugh, and thanks to the media, it's harder to deal with that. Thei mage of perfection in models is often false, even. Pictures get retouched, makeup, which is unnatural, accents their features, they pay thousands of dollars an hour for fitness trainers, too...
Don't let anyone bother you about your body image, especially how your breasts look. That is something you have nearly non-existant control over, and they would look very immature for being insultive for that.
And as a closing arguement, I am sure more women have imperfect breasts than perfect ones.

Underneath clothes, more people go against the image of beauty than they first appear.
I suggest making yourself feel beautiful in a less expensive way than surgery, and a better investment. Maybe setting a reasonable goal for your body, and durign working toward that goal, be saving money to treat yourself to something nice, like nice sleepwear, if you know what I mean. If you go to sleep beutiful, you wake up feeling the same way. That's what I am doing. I am going to even lose more weight and then buy some beautiful clothes for myself to keep me motivated to keep the wieght off. I won't gain it back if my money and clothes end up being wasted. ^-^