I am another who had concrete floor. Put down 2x4 sleepers flat, some 1.5 foam insulation and regular 3/4 flakeboard subfloor. So much more comfortable during winter (in Colorado above 6000 feet). Personally, I like a little bit of springiness in floor. Have a job where I’m often on my feet for 8 hours on concrete and my feet and legs kill me. Can spend 12 hours in my shop with no pain. It’s a shop - never did anything to finish floor, just the bare flake board.