You asked

How will breastfeeding change the appearance of my breasts?

Your breasts are affected by many factors. Their appearance, size and shape can change due to weight loss, weight gain, ageing, and of course, pregnancy. Breastfeeding does have an effect on how your breasts look and feel.
Your breasts become larger and your areolae will have a larger surface area and become darker. Once your milk starts “coming in” after your baby has been born, your breasts will increase in size and weight. After two weeks, they will become slightly smaller, basically the same size that they were during pregnancy and they will stay this size until your baby has been weaned.
After weaning, your breasts will return to their pre-pregnancy size, but will not necessarily be the same shape. They will have lost a bit of “perkiness”. Firmness will also be lost and your breasts will feel a lot softer inside. For most women, this trade-off is worth having a healthy well-fed child. Bear in mind that your breasts can only stay unchanged if you never gain weight, grow old, or become pregnant.

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