changing platform floor to cut in floor

I have a very old (1897) Jarrah framed house in WA and I want to do some remedial work on the isolated brick piers which necessitates me removing the floor. The floor appears to be platform jarrah boards. Someone casually told me a few years ago that I can set my circular saw to 12mm and cut the floor out at the perimeter. However, I feel unsure whether I can re-insert the floor as a cut-in, as the non-external walls are sitting on single jarrah joists, only the externals are on double joists, which to my mind, would not guarantee me a nailing space.

Is the usual solution to nail on some timber to the existing joist, to allow for re-nailing of the now cutin floor? If so, any caveats on this solution?