If the hardwood is in good shape and you don't want to have to sand and refinish, I would recommend covering with the floor with red rosin paper (tape the seams to keep it in place), then a layer of carpet padding and finally a layer of 1/2 plywood or OSB. This will protect the floor from scratches and dents should any larger chunks of wood, plaster or drywall (or tools) fall on the floor.