No co-sleeping let them sleep safely in their own crib preferably in their own room away from you with a monitor. I like a sound monitor and my owlet. Cameras can't really tell you anything but the owlet lets you know if their O stats drop and that is the biggie in my book. Not 100% but an extra safeguard. Even if rolled into the hallway out of the line of sight really is the key, if you have a nook in your bedroom that will work too. Closer to 6 months the sleep gets interrupted and self-soothing and falling back to sleep is harder because of the shared space and interruptions (rolling over, snoring, getting up to go to the bathroom etc.). They see mom and dad and want to play!!
All I mentioned above but even more of it. This age babies learn what to do to get whatever reaction they want from their caregivers you can start seeing stark differences in their behavior between various caregivers. They have figured it out. This is also the stage where separation anxiety kicks into high gear. Google 'separation anxiety' and use those tips. It is a hard phase, but if consistent you both will survive with your sanity and eardrums intact :) If you can start daycare right before the 6 month mark it will make everyone's life easier. Even part-time mothers' day out programs are a huge help.
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