I'm pregnant with asthma and my nose is always stopped up (even b/4 pregnancy). I want to buy an humidifier but what kind?

Save your money. Humidifiers may provide some relief but they also encourage dust mite growth so if you are allergic then this is not a durable solution. Most women don't want to take any medicine during the 1st trimester. Nasal saline is safest but some prescription nasal sprays are not so bad. It is imperative that your asthma is well controlled. Risking Fetal hypoxia is far more dangerous than asthma meds.