My latest development in growing has been a foam insulation box. To heat, I used a fish tank heater in a large jar. I used an ultrasonic humidifier with a valve on the outflow so I could precisely control the humidity. For fresh air, I had a small fan with a hepa filter that blew air into the box.
It was a pain to learn how to use, but once I got the balance of heat, fresh air, and humidity down, it worked pretty well! Took a bit of effort to constantly adjust for changing conditions, though.
Be an adult only when necessary.