1. Remove the floor and install a plywood subfloor in its place.
2. Screw down the pine floor along the sides with two screws on every floor joist. Then install a plywood overlay on top of the pine boards to take out the bounce.
The most critical factor for you is to make sure that the floors are level with the other floors that it will butt against. Me? My choice would be #1.
Do not use regular nails when laying the floor. Use annular ring or drywall screws for a much better hold. Have Fun!!!!!
say that the floors bounce. In a 108 year
old building, with that problem, I'd welcome
the opportunity to get a look at the joists.
There could be old termite damage or rot.
Wood can get weak and sag when it gets that
old. Check them, and you'll know for sure
that everything's OK.
Count me in on this one. Do the job right the first time. You might want to sister additional floor joists alongside the exsisiting joists. A couple of bucks maybe, but worth it. Also, you could use tounge and groove subfloor. Glue it down with construction adhesive and screw it down.