I was looking into this myself as sometimes struggle with air being really dry.
In the end I’ve opted for an air filtration device instead of a humidifier …. and that’s made a huge difference to air quality.
The biggest thing for me was the reviews I read which said about mould build-up in some of the cheaper humidifiers which effectively then is just releasing that into the air.
Some of them seem to be due to them being difficult to clean cause of design etc, and I read somewhere that a pan of boiled hot water does the trick just as well (obviously there are safety considerations if using it in a baby’s room) but certainly gave me food for thought and put me off buying one.
So while I can’t reccommend any specific humidifier I would say the biggest consideration is looking at reviews and seeing how easy it is to clean because if you can’t clean the inside properly you risk then having what is effectively dirty water vapour being introduced into the room which is something you’d want to avoid of course.