Keep in mind that the ventless heaters are using the same air you need to breath. If you always keep the door open during working sessions, not much of an issue but if you keep the door shut, could become a fatal issue. Plus those same gases can get into the main part of the attached house. Not uncommon for part of a split house system to be in the garage making the bad vapor issue even worse. Whatever you do, include CO detectors for the main house.
Something like this:
https://www.homedepot.com/p/Williams...621A/100118902
A simple box fan or similar serves to move the hot air around. Had a similar version in a 10x20 garage that would way over heat the place if you turned it up very high.
Nice thing is it doesn't need electricity so can serve as an emergency heater during winter power failures.