Unfortunately, there is not a lot that we can do to alter the way the breast tissue changes during and after breastfeeding. These changes are mostly due to the fact that once a woman has completed breastfeeding, the ductal lobular units of the breast that make and transport breast milk involute and decrease in volume.
Additionally, the ligaments of your breast, called Cooper's ligaments, can become stretched out during pregnancy and breastfeeding. These two things together lead to a decrease in the volume and perkiness of the breast tissue.
Some women report that wearing supportive bras throughout pregnancy and breastfeeding helped prevent their breasts from sagging after breastfeeding, but this may be more effective for some women than others.
During pregnancy, breastfeeding and beyond, women should avoid rapid weight gain or loss as the amount of body fat a woman has correlated to the size of her breasts, and rapid fluctuations in body fat can lead to rapid fluctuations in the size of the breasts. These fluctuations can have a negative impact on the integrity and elasticity of the breast tissue.