I am not going to sell you a sleep method. I will tell you what changed things in our house, and you can take what helps.
The same three steps every night
Bath, feed, song. In the same order, at roughly the same time. It took about two weeks before it seemed to mean anything to our daughter.
Dark and boring at night
Night feeds happened with a small lamp and no chatting. Daytime was bright and noisy. Slowly the difference sank in.
Taking turns
We split the night into two shifts so each of us had one long stretch of sleep. It made us kinder to each other.
Safe sleep guidance changes from time to time. Ask your clinic for the current advice.