Go with the sub-floor heating if possible. It will be the most comfortable.
It could act as a zone off your current system, or you could investigate setting up a small-scale geothermal loop where heat is extracted from deep underground, released into your floor, and pulled from other parts of the house when the summer kicks in.
If you’re going to be doing any power excavating, it should not be too much additional cost. A vertical bore for geothermal extraction doesn’t even leave a large footprint.
The advantage of geothermal heat is that even though it’s driven by electricity, the heat source is well above freezing, as opposed to air-to-air exchangers which have virtually no heat content available in your climate.
Good morning, Bob.