If your temps drop any more I'd say yes get something for heat. Even a small under tank heater would help. I force my place to get to 70. We lost power last summer and I got scared my place was going to cook my guys, I had to emergency move everyone to my truck and my girlfriends suv and bring them to a friends. It hits temps of 120+ here and we hardly get to freezing. As far as your misting issue I would heat the water on stove to 80-100 any hotter and your plastic in the squirt bottle could release some toxins that might or might not do something. (why risk it, I know it's debatable but still) and use that. If you do end up using a heat source remember to use some sort of item to limit heat (ie. Thermostat, rheostat, or dimmer). You don't want a malfunction to occur and loose a dear friend, or scar them. Your not going to need a lot, although if you throw a potted plant like pothos in the tank it would enjoy the light as well. My cresties tank has a couple plants in with them. So I have a plant flourecnt light with 2 cfl grow lights. I just have slate tile for the bottom I have some bleached cholla segments in there with large openings for them to climb about and a few other branches spread about. I keep a large water dish like 8" diameter in there to help with humidity (we have an average of 10% out side on the high side) but I keep it full of stones so it's not to deep and usually a branch of the pothos is in it as well.