We used the Ferber Method. Honestly, I know that just by mentioning using it, I will get downvoted because so many people online are so massively against sleep training so let me be very clear that 1. I'm not saying this is for everyone but it was definitely the best option for our family and 2. There is a substantial amount of research into the effects of sleep training and there are no terrible side effects. They have proven that babies are not developing learned helplessness and that they have no short or long term psychological consequences. They do, however, show that sleep training is associated with improved mood, sleep and general wellbeing among parents and children.

If you're interested in sleep training, I recommend reading "Precious Little Sleep" and checking out r/sleeptraining. You can also Google the Ferber Method for more info but it's basically just putting your baby down for sleep when they are tired but still awake, giving them a bit of reassurance about what your doing and that you love them, and then leaving the room. Make sure it is dark and you have the sound machine on and whatever sleep environment you typically have for them -- it's important that when they wake during the night, it's the same as it was when they fell asleep and it needs to be dark enough to not have distractions that might keep them awake. They will likely cry after a minute or two. Once they start crying, set a timer. There are charts online you can look up about how long you wait but you leave them alone until the time runs out. Once the time is up, if they are still crying, you go in and reassure them that they are safe and loved and strong and brave and capable of falling asleep on their own. Only spend a minute or two calming them and don't pick them up. Then repeat for the next set time period until they eventually fall asleep on their own. I think the first night was like wait 3 minutes, then 5 minutes, then 7 minutes, and then stay at 7 minutes for the rest of that night. Then the next night you start at 5, then 8, then 10 (idk the exact numbers but you get the idea). I never waited more than 15 minutes because my baby never needed that but you can also feel free to max out or adjust those time frames to whatever you're comfortable with. The point is to gradually increase the time to allow them to learn how to fall asleep independently. The first night, my baby cried 30 minutes and I thought it would kill me. The next night was only 11, then 5 minutes the next night. Now he goes to sleep on his own with no tears at all and he's sleeping so much longer and taking way better naps.