Another thing I would recommend is placing the pot over a propagation mat to keep the roots warm. During late autumn, winter, and early spring, I had the banana plant under or near a 1000 watt metal halide light. The light was on for 12 hours a day. The plant is now too tall for the place where the light can be mounted, so I recently took it down, a move I'm sure was not welcomed by some of the other plants in the greenhouse. Our weather lately has not included a lot of sun.
Temperature is important.
Bananas will stop growing when the temperature drops below 53 degrees Fahrenheit. We had one night last winter when the temperature dropped to 11 degrees. I managed to keep the greenhouse at 59 degrees even then. On the other end of the spectrum, the growth of bananas slows above 80 degrees and stops altogether above 100 degrees. For the summer, I have a mist system that cools the greenhouse air to the temperature I specify.