Comfortable humidity for Baby's room

[dariusptrv]

Our son will soon be 3 years old, so we are preparing a baby room so that he can sleep on his own. I would like to know what humidity should be in the room? I searched the internet and it says from 50 to 70%, but in our apartment this value is on average 30-40%. I guess it's too dry. Please share your experience. What humidifiers are best to use?