My wife and I just bought a home and were planning to re-floor throughout. Upon pulling up the carpet in the master bedroom (second floor) we discovered what we initially thought was hardwood. Upon further inspection, it’s a tongue and groove pine subfloor that somebody “finished” long ago. We are trying to figure out our best options for replacing with OSB without causing any compounding issues.

As far as I can tell, the wall isn’t consistently sitting on the subfloor. looks like there is some sort of sill plate sitting directly on the joists, but hard to tell without tearing apart the plaster walls.

We are hoping it may be as simple as pulling up the pine and adding some blocking before re-sheathing in OSB. Any pro advice or experience with something similar is appreciated. Thanks!!!