Once you stop or reduce feedings to once a day (for ex. At night only to comfort your 1/2 yr old baby who doesn't actually need it anymore) they lose all definition but it's not like your skin goes back. You're left with breasts that are akin to golf balls in Walmart baggies. Not cute but apart of mother hood for 95% of us.
I’ve heard saw palmetto helps but you could also just wear a padded bra. And remember, the bigger they are, the more there is to eventually sag haha.
One thing I wouldn't do, personally, is get implants. Just about everyone I've known or known of who got them had to get them re-done or removed sooner or later, for one reason or another. It seems the body just doesn't like artificial imports and tries to reject them. So it's not like you're just in for the one surgery and can figure you're done with it after that.