Recommendations for radiant floor heating over existing concrete slab?

I live in AZ in an adobe house built in the late '30s. There is no foundation, just a concrete slab directly on the Arizona dirt. I know heat rises, but it radiates through solid contact quite effectively, and my concern is the earth beneath my slab will absorb some of that heat. What would you recommend as the most cost-effective, sensible solution to heating my 1200sqft house? The roof is not up to modern codes and I hate the idea of sticking a heavy heat pump up there. It can get quite cold at night in Tucson (sometimes mid 20s) but it is RARE that the daytime high is less than 50-something and usually even warmer. Is radiant floor heat even an option on an existing slab? I plan to tile or laminate/hardwood the entire place. How much height will the tubing/elements and thin set add to the floor? Do I need to add a thermal barrier over the slab before installing? I don't want to add so much height to that floor that I have to redo all my doorways. Thanks for knowing what yo
u're talking about before answering this question.

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