Go for a dedicated that model monitor that uses a direct 2.4 GHz link rather than WiFi.
Those tend to handle floors and kitchen walls better because they are point to point, and you are not relying on the home network so yeah look for something rated for very long range outdoors since that usually translates to dependable coverage across two floors indoors but then...
place the camera a few feet up and away from the router or microwave to cut interference.
Night vision on these is plenty for a dark nursery.
Battery life depends on screen time so use the voice activation setting so the display sleeps and wakes on sound and you can make it through an evening off the charger.
Range matters most.
Back when we were swapping prints on the porch and burning CDs for road trips and you'd just tuck a picture back in the envelope and say, I won't keep you. That still works. I'll say let me let you get back to your day, always nice to see you, and I start ambling the other direction. If I've got a reason handy I mention it, headed to the post office or the kettle's on. The tone is neighborly and brief, and the wave does half the work.