Advice on sleep training?

Ky • Married to my best friend👩🏾❤️👨 Living in Europe Mommy to Marcel 🌈👶🏽

My LO is gonna be 4 mo in a a couple days and he's been sleeping with my DH and I since birth. He slept in his bed for naps and sometimes at night in the beginning but it was easier with breastfeeding so we just kept him with us. I will continue to bf but will introduce formula for night feeding because I heard it helps, my bub is still waking up every 3hrs. Any advice on what's worked for you mommas out there.