What worked for us was cry it out. It took 5 days, was very tough , but even on the first night the number of wakings had reduced. By night 5 DD was sleeping 12 hours a night.
Joy returned to our home! Dd was so much happier and smiley too - babies need their sleep too! For the first time I could actually enjoy her and being a mum! It was profound, wonderful, amazing, the difference to us all.
I'm not saying she never woke up again, but We never had to repeat that process. She woke up if she was ill or in pain or there was actually something wrong. It was manageable.
I recall some issues when she moved to a proper bed and so could get out. But by that age she was old enough to be reasoned with and have stickers or whatever for staying in bed. No crying involved at that point, and it was more in the evening putting her to bed and then her appearing again downstairs that was the problem, rather than night waking.
DD is 7 now and not showing any ill effects from the 5 days of sleep training. We have a great relationship, she is funny, bright, caring and happy.
Good luck!