Are you pumping milk? If not and baby is latching, then try pumping after feeding so you can give breastmilk bottle after boob, and if baby still doesn't seem content then you can try a little bit of formula. Always do pace feeding with slow flow nipple. There's nothing wrong with supplementing, but if you are serious about breastfeeding then formula should be the last resort. My boy is 1 year old in just 2 days now, we are supplementing since 5.5 months, he stopped latching just a week before 7 months, since then I'm pumping, but my milk always comes first and he gets only as little formula as possible, because he gets a super expensive special thicker version of formula and even that makes him throw up