MrsJ, you can take garlic and it will come through the breastmilk. Breastfeeding is a great way to dose little ones with beneficial herbs. Not as potent as a garlic poultice, but still helpful. Garlic thins mucous.
Coconut oil on the nostrils, just a bit, helps keep the nose from crusting, too.
A cut onion near the crib is said to be helpful for easing nighttime breathing.
A good, gentle nose washing from the outside only (not nasal irrigation), finishing with a gentle squeeze on each nostril (start high on the nostril and squeeze downto the end of the nose) to clear out the mucous is helpful, too. Baby should be upright or tilted to the front. You don't want water going up the nose!