Dry air in house

Winter is always dry and harsh I live in upstate New York but my poor baby is getting so congested / coughing every night. We went to the doctor Wednesday because of it, we’ve been using a cool mist humidifier but it’s definitely not doing the job. I wake up constantly with a raw throat and my 2 year old has a wicked cough. What else can I do? I told my husband to change our vents and lower heat at night