Need heating in my outdoor shed

They are so much cheaper and a quick fix

My outdoor shed is an awesome location to workout. I have an more than seven foot ceiling, twenty length and a twelve width in there. I have just enough space to kneel down more than one folding mats and be comfortable. Along the side I can tuck away my bicycle, speaker method and jump rope. It is a cozy, cute little location to labor out. I spruced it up by adding costly switch plates, bright aqua paint and a current light. It entirely looks prefer a fun location to exercise. The only thing is that the shed isn’t properly insulated. The walls and ceiling have none and it shows. I added current windows that help somewhat, but are not a real fix. In the wintertime I have observed that I entirely freeze to death. I try to wait to labor out and I keep the door closed to retain my body heat. That only takes myself and others so far. I looked online at ductless mini splits and they are so expensive. It would labor perfect for my needs though. The indoor air handler would mount on the exterior wall and connect to an air compressor outside. I would have a control equipment and the ability to heat or cool the space. I could even get a smart control equipment and start the Heating plus Air Conditioning equipment before I am in the building, for right now I am looking at space heaters. They are so much cheaper and a quick fix. I don’t believe it will be the magical cure I am looking for, but it will help in a jam.
Duct sealing