Breastfeeding doesn't have a lasting effect on your body shape.
Any lasting change to the shape of your body or breasts after becoming a mum is far more to do with muscles stretching during pregnancy, your weight going up and down before and after the birth, or from not wearing a supportive bra during pregnancy and/or breastfeeding.
Your breasts may seem very full in the first days as your milk 'comes in,' but they'll soon know how much milk to make and reduce to a more comfortable size. They'll go up and down with every feed as they fill up with milk and are then emptied by your baby.
When you stop breastfeeding, your breasts may seem a little droopy, but they'll perk up again over the following months as fatty tissue begins to replace the milk-producing tissue. Make sure to wear a good fitting bra to avoid any lasting effects. You can find out what to look for in our page 'Getting a new bra'.