You could always go down the heat pump route. Heat pumps are ‘always on’ so it should always be warm.
Then do what I did. I installed 30kwh of lithium phosphate batteries (coupled with supercapacitors in parallel) in the shed. They are kept charged up with solar on the roof and a tiny domestic wind turbine in the garden. The heatpump is then dual fed, by my batteries primarily and then the mains/grid as secondary. When the batteries run dry (which they haven’t yet done due to the bright sunny weather this winter) the grid will supply power to the heatpump.
I have no more heating bills and I should be future proofed for the next 8-10years.
Tell us about the domestic wind turbine please! Cost, size etc..