If you have reached iron age ( able to get iron) you can use iron-reinforced beam in your floor construction and place a fire on top of that beam...

https://steamcommunity.com/sharedfiles/filedetails/?id=2660552367

https://steamcommunity.com/sharedfiles/filedetails/?id=2660552470

https://steamcommunity.com/sharedfiles/filedetails/?id=2660552649