We have a cabin in the woods on our mountain property that I was converting into a music studio. The cabin is about 20' X 15' and during the reconstruction, it was fully insulated, including under the floorboards. It had 110-volt electricity but no plumbing as it's too close to the property line.
After much research and discussion with builders, lumberyard advisors, etc., I came to the conclusion that electric baseboards were the only viable solution. The cabin had to be rewired for 220-volts and the radiators have variable (manual) thermostats.
The biggest problem occurs during the night when it gets cold. The "bones" of the building and everything in it get cold if I turn off the heat. Then it takes a long time to heat back up. But if I leave it on at night set at, say 68º, it wastes too much electricity. My solution has been to set the thermostat at about 60º at night then it only takes a half an hour or so to get comfortable. It's a little bit of a pain but so far, it's worked well.
The cabin also has a small Malm fireplace that heats up the space fairly quickly and gives the cabin a cheery atmosphere. If you can add an enclosed stove, like a Jotul, you can cut your fuel/electrical costs significantly. Here's there website:
https://www.jotul.com
One thing I definitely recommend: Do not leave your space heater going all night unattended. Even if it's UL-Listed, that's a potential danger and I'll bet the owner's manual recommends against that practice. As I've been told countless times, Safety First!
Good luck with your studio!