Not sleeping through night

She is 20 months old and WILL NOT sleep through the night. Never has. She is put down about 8:30 and wake up anywhere between 12-3 am and goes right back to sleep once she gets a boob or a cuddle. I have tried letting her cry it out 20 min but after that I just feel its to long. My first child I had fully sleep trained at 6 months to sleep through the night and self console if she woke up!! I have another baby otw and I NEED SOME SLEEP. Co sleeping is not working because we have a queen and she is a horizontal sleeper. Please send advice 😭