The question of a battery powered light comes up two or three times a year, and the short answer is there aren’t any because the light requires too much energy and you don’t have enough left to run a radio so it can talk to SmartThings.
The longer answer is that there is one, the Phillips hue go that you mentioned, but in order to save its own battery it turns itself off after about two hours when it’s not plugged in and then you can’t reach it from the network anymore until you plug it in again. So it’s a good party light, but not for the kind of situation you describe. Plus it’s really big, about the size of a popcorn bowl.
My own solution for this kind of thing is simply to have another outlet installed high on the wall. People do something similar for wall sconces anyway. But that way you have all kinds of options, including adding a babycam. In my neighborhood the regular price to have an electrician do this is around $150. It might be less expensive in some places.
Then if you want to really simple solution for the device to plug into it, the Homeseer HSM 200 is a zwave nightlight with eight different possible colors that also has a light sensor, temperature sensor, and a motion sensor built-in. I know some people have put them in kids rooms and just put daisy petals around the light to make it look ornamental. Obviously your project is much more ambitious, but it might be a good fit.