As its an old house most likely the floor beams are tied into the party wall and most of the sounds will be travelling through these and up out of your exposed floorboards, just as much as straight through the party wall itself.

Lift the boards and pack the void between the beams with dense rockwool, and fitting underlay and carpet will also help, not as trendy as exposed boards but I doubt you will be bothered at 3 in the morning.

The other thing you can do is lift the boards and add strips of rubber to the joists and then relay the boards on top. Another old trick is a layer of dry sand onto the plaster under the boards to dampen the vibrations.