Hey Juliana- As far as what I did to lose the weight, honestly I tried just about everything but I think either weight watchers (which I did a little bit) or just watching calories in vs. calories out (majority of what I did) would be the way to go. Luckily, at our ages, our skin is still pretty elastic so depending on how much you have to lose, you should be fine. But always remember, its not just about a clean diet and cardio- WEIGHT TRAIN!
If you just lose weight via clean diet, you become what some people call "skinny fat" whereas if you build that muscle you will burn fat faster and perhaps weight slightly higher than your goal weight but look a lot less than that number.
As far as my boobs, lol they're fake. I was born with a condition, which with all the extra weight never was really noticeable, but once I lost the weight the tubular breast became really apparent- so I opted for a boob job.
Honestly though, sagging in the breast and decreasing cup size with weight loss is almost inevitable, but be sure to do pec exercises which will help with the sagging and building the pec up underneath will help a bit with giving the illusion of a bigger breasts.