@philosopher Have you had wood floors in the past? I ask because you seemed worried about the floor as though it is wood.
The rubber things we have are not glued, they kind of just fit over the bottom of the leg. I have no idea where we bought them. They don’t really look good though, you can notice them.
I recommend you take a spare tile and try to scratch it up. I think after that you will feel confident you don’t have to worry. I had porcelain in one house, never worried about it, never had a problem.