It's actually not as bad as it seems. I converted the attached garage a few years ago by replacing the large door with a doorwall, which faces due South. Most of my plants are dormant or semi-dormant in the winter, I just put them out there and barely heat it tp about 40 degrees, water about once every 2 weeks, and they sleep away the winter.
The only issue are the truly tropical plants that can't take cold temps. Those have to come into the main part of my small house.