Help! My 1y2m old baby is underweight

Help! Underweight na po si baby for his age (1y2m) EBF kami for 1 year. The moment he turned 1, I decided na i-mix feed siya kasi papunta na siya sa underweight. Malakas naman po siya kumain ng solids, but formula milk, no no talaga. He intakes 1 bottle per day, kailangan kutsara-in pa. At night, malakas naman siya dumede sakin (I can only breastfeed him at night, kasi I'm a working mom) Ano po kaya dapat ko gawin para mapainom siya ng formula milk while I'm at work? Kailangan ko na po bang awatin ang pag breastfeed ko sakanya? Thanks!