Thought I'd post an update here just in case anyone else has a similar scenario. After much mulling, and some chat with a structural engineer, we ended up with felt like the best compromise that didn't involve either dismantling half the house's existing framing, or...
That was my first thought as to the best approach, but I'm wary for a few reasons:
The right 3x2 (in my diagram above) goes under/into the fireplace structure in the corner of the room, and the trimmers around the hearth are being held up by it. So a) I'm not sure I can remove it and replace...
Working my way through renovating a Victorian terraced house atm, and have progressively discovered issues with the floors in every single room. Nothing too crazy so far with most of the joists - replacing some rotten ones here, jacking up and sistering some sagging ones there - but the final...