Sure you want to destroy the original floor boards? They don’t look that bad? Surely a thick underlay and then the carpet would sort it? Worst case you could sand them level first?
They pretty warped on the profile, you can't see it from this photo but you can definitely feel it under foot. Your idea about a sander will probably sort that out a bit, in addition to the over-boarding.
Sure you want to destroy the original floor boards? They don’t look that bad? Surely a thick underlay and then the carpet would sort it? Worst case you could sand them level first?