Fisrt a ceramic tile needs a subfloor that won`t move you probably don`t
have one, concrete board should be used it is the thinnest strongest
material for tile, even joists can be weak , rotted . Take everything
out, old baths often have rotted wood that has to be fixed first.
Honestly you could have a major job but won`t know till you look . This
could be a reason it is not tile now. Get out a pro to give ideas ,
better then finding out the worst is a total redo.