Underground house flooring

Hello everyone, my husband and I are in the planning stages to build an underground house. We live in Maine with our 4 kids and winters here can be brutal. Our house was built in 1880 and has made us very cold during the winter months.

So we are going to build an underground house this year! However, where we want to build it we cannot get a concrete truck in there. We want to leave as much of our land Undisturbed. We have been researching extensively but cannot find and alternative way to do flooring other than concrete. We do not want to have dirt floors in our house. Does anyone have any wisdom or knowledge they can share about this topic? It would be greatly appreciated by our family.

I asked sort of the same question a couple yrs ago, though still don't feel I know what I am going to do yet so very interested in what answers you might get. Especially since I am planning to start clearing the pad where I am going to build this spring. So it is time for me to figure it out myself.

If you want to check out my old thread https://permies.com/t/62429/wofati-earth-shelter-home-floors

Well since no one else has chimed in yet.

Some of the ideas I have been considering is:

stone, I have a lot of granite on my property. The hills are shedding it like crazy and I could collect a lot just right around my build site.

wood, like the wofati pic I showed in my thread a little spacer to keep the wood off the earth, then some nice wood planks to make the floor. I would probably try using stone or brick to raise the floor off the earth.

cob treated in boiled linseed oil. I know you said you don't want dirt floor, and cob technically is. However cob is a different sort of earthen floor especially after treating it with linseed oil. At that point it is more like an earthy concrete.

Then I have considered mixing of two or all three.

I still haven't decided yet though and still doing more research. So if I find some other options I will post them here for you as well.