I live in a one-bedroom apartment (640 sq) which has two furnaces (they cool in the summer/heat in the winter). The air gets so dry in the winter, that I thought it would be best to purchase a humidifier for the entire apartment, but I am having a very difficult time knowing what to purchase. I can't attach anything to the furnish, and I don't want to spend over $100. Should I get "cool" or "warm" air? Is a "medicated" option worth it? How much of a hassle are filters as opposed to all-in-one units?