Back in the house, the dining room floor has now been almost completely taken up - just the bits around the gas and central heating pipes to negotiate. Depending on the cost, we may well replace all the joists too, rather than just the obviously rotten ones. This would make it easier to shovel all the crap out from underneath, they could be better supported (at the moment the joins are sitting on wobbly piles of bricks); we wouldn't have to worry about all the old nails when laying the new floor, and it would be easier and more effective to buy pre-treated timber than to treat the old ones.
I think I will then go for reclaimed pitch pine boards (like on Warrior!) direct onto the joists, rather than laying new boards and then flooring on top. This should enable it to breathe better, and the height should be roughly the same as the sound boards in the front room, which I am probably going to have sanded and oiled as they are mostly aesthetically OK as well.