Oh My! I sincerely hope someone can offer you some practical solutions.

Glazed porcelain tiles are so very slick & slippery. Surprised the tiler didn't dissuade you, especially for a MBR and someone with MS.

For now, I do agree with the rubber-soled house shoes. Even barefooted there's a major slip factor, especially if your feet are wet. Personal experience speaking here and I'm barefooted all the time...

YES.

There are coatings which can be applied to greatly increase the slip resistance. Be aware this will make the tiles a little harder to keep clean.

The tile people sell tile. They don't give a ____ ___ about what happens the moment the tile leaves their doorway.

To get the proper recommendation, head on over to the John Bridge Tile Forum and ask the Pro's for their experiences with the limited number of products available.