L.M.
Here's a couple links that I hope will help answer your questions about humidifiers.
http://life.familyeducation.com/baby/parenting/40590.html
http://www.articlegold.com/Article/Warm-Mist-Home-Humidif...
What I use, can be used for anyone of any age, is putting vicks on the bottom of your feet before bedtime, cover your feet with socks and that will help with the coughing. It's amazing how this works!! My little one also had a pnemonia and it worked wonders with her cough.
L.