I've read how many successful Oehler style PSP structures use earth, poly, carpet.
My question is how are these floors with bare feet in the wintertime? Do they seem too cold?
I was thinking about floor insulation using natural materials like straw. If the floor was earth, poly, straw, poly, carpet; then the straw would be protected and might last for decades...
I also think radiant floor heating might work far better in Oehler structures than in structures with a concrete slab. One inch diameter poly pipe costs about $.25/ft. You could use 1 foot of poly pipe per square foot of floor. It would not take too much work to bury 1" diameter pipe as shallowly as possible and level the earth on top of it.
I would terminate the floor pipes in easily accessible places with good valves. That way the design could connect to any heat source, solar, wood,
compost, geothermal, whatever. If the house was split level, I might give each level its own separate radiator coils. I would gladly accept the sight of poly hoses running along the interior of the house, in order to permit flexible complexity.