It’s also worth raising the bathroom door threshold by about 5mm from the floor in case the room fills with water (if someone covers the shower drain with a towel, for example). This will keep the water contained.
Be practical and take advice on whether your floor will take the weight of a cast-iron bath, as they are very heavy. If it won’t, then composite or acrylic versions are good alternatives. If you decide to place your bath near a wall or window,