I sleep with a Himalayan salt lamp on. It's soothing and relaxing. It has a little cup on top to put essential oils into to disperse. It's beneficial in multiple ways and is in no way childish.

Keep your nightlight if it makes you happy Even if it's childish!

I also sleep with stuffed animals and blankets sometimes. What's wrong with comforting yourself? We're supposed to be meeting our own needs anyways.