There is treated wood that can be used for foundations. "Modern" wood treatments come from very old technologies. Most I saw came from15th/16th-century barns and shipbuilding techniques - seems you could research and use treated wood as the foundation.
https://www.nachi.org/permanent-wood-foundations.htm
Of course where you live/climate would need to be considered with other drainage, stability issues, etc.
When I lived in the desert I considered a cured earthen floor.
Earthen floors can be very beautiful and durable. best of luck with your plans.