I've got the original pine floorboards in my Victorian house. I'd like to keep the original floor but change the orientation by 90 degrees. One option would be to lay 12mm ply on top of the joists and then relay my floorboards on top. The downside is that the floor level would be raised by 12mm and then I would have to re-install the scirting boards . The other option would be to install noggins between the existing joists or install the 12mm ply between the joist so its all flush. What wold you suggest?