Unless you're using kviek, the yeast will be fine. It'll be slow but fine. If you're worried, test your gravity at your normal ferment period (I usually do 2 weeks) and then give it an extra week and test again. If it hasn't moved, you're done fermenting. Heck, you could leave it a month longer and still be ok. There are always tales of "I left this in the back of my closet for a year, is it OK?" and it turns out fine.

You could get a heating pad, or maybe get a bigger barrel and fill it with warm water (although you would have to keep adding more water as it cools).

Go out and buy a hydrometer. And then actually measure the specific gravity.

If the specific gravity is dropping, then your beer is still fermenting regardless of how much "bubbling" it's doing