Interior sill "chequer", "diamond", cover
Years ago on one of my 97's I had found and installed interior sill "protectors".
They covered the inside "lip" of the sill, did not require any drilling or anything and were kept in place by the 3 or 4 bolts that you see when you open the door. I remember really liking them because they protected and could be taken off at a moments notice and did not require any modifications to the 90.
Think an "L" shaped piece of chequer plate. About an inch or so on each side of the "L". and they ran the length of the inside of the door. They were awesome and I can't recall where I got them...