Most breastfed babies don't require a soother because they naturally get enough comfort sucking at the breast. Soothers were invented for bottle fed babies because, when full, they may need more time to suckle. During breastfeeding, suckling happens naturally because the milk flows more slowly at the end of a feeding. This gives the baby time to suckle for comfort and not get a lot of milk; her hunger and sucking needs are both met. It's an all-inclusive baby resort!
If you find that you need to use a soother, it is best to wait for at least a month before introducing it. Giving babies soothers or bottles before they have learned how to breastfeed can be confusing for them. Give your baby a chance to learn one thing at a time.