I don't want to buy any synthetic teethers/soothers. Any suggestions on homemade/natural teether or soother?

You can make breastmilk ice cube for your baby. Simply put the breastmilk in a ice cube tray, keep it in freezer and offer the breastmilk ice cubes to your baby. Cold ice cube can help to soothe baby's itching gums during teething. Let your baby chews and sucks.