Greenish stool suggests inadequate feeding or starvation.
Always empty one breast before switching to another.
As for the mucus, kindly pay attention to your own diet and avoid herbal remedies or drugs that are not prescribed by the doctors which may pass via the breast milk to affect the baby. Avoid heavy spicy or flavored foods as well as some also affect the baby when passed via the breast milk to the baby.
If the mucus persists in the stool kindly see a paediatrician.