Sorry hun, boobs are pretty much just inner workings and fat. As the number on the scale gets larger and smaller, they do too. As for the bum, you can work the muscle to make sure it is nice and firm to retain the round bum you like, just a bit smaller.
Go here to find a list of excercises to target your behind - http://www.freetrainers.com/exercise/musclegroup/buttocks/