Given the choice, lift the plants up first of all. That's very important.
Drilling side holes was a good call.
You may still need a space heater, but first things first.
6 feet tall huh? Ehhhhhh that's a BIG plant for indoor conditions. You need to get them into bigger pots- they WILL double in size at least over the course of flower. Try a large feed-bucket, at LEAST 10 gallons. Or a kitchen-sized trash bin with lots of holes drilled in it. OR a rubbermaid tub. As long as the pot isn't metal.
When you re-pot, use plenty of perlite. This is even more important in colder conditions. Cold but dry is much safer than cold and wet for plants as well as humans.
A slab of that same insulation that's on the walls is fine on the floor to protect them from the cold.