Your floor moves when you step on it. At some point the blades are disjoint. Your house is old. If the floor is original then try to tighten all the screws or nails to add. Seal the cracks between boards with string. Feed him the floor with del'huile flax and gasoline Turpentine (1l of turpentine for 5 tablespoons of linseed oil).
You could also sprinkle talc, and integrate into the interstices to stiffen your floor
Be aware that wood is a material that works and then moves. The solution for some time: disassemble and remake
Hello, I did not interpret your message as lds, I realized that you wanted to replace 'existing new! If you must make your own work and have enough ceiling height, there's no photo, renovating over the existing. After following the explanations of Ids, do a patching, place a layer of soundproofing and rest, such as a floor syntetic, which offers a wide variety of colors and veins. If you must remove the existing floor, be aware that due to the construction technique of the time, it is likely that the partitions are placed on it. The work is of course feasible, but does not raise some concerns. Please keep us informed