I could go on and on about posture, but I won’t. It’s a lifetime of learning and correcting. Plus, there are many schools of thought. I will only say one thing:
Shift your weight toward your heels.
Not 100% in your heels. Your footprint should still make contact with the ground. Just shift your weight from the ball of the foot towards the heels. Feel the pelvis relax and untuck, the ribs relax and flatten, the neck relax as the head comes over the natural support of the neck. Just start with this foundation.
After 10 months of pregnancy, breast feeding, carrying heavy little bundles of joy, the body adapts, and we need to reclaim our posture.