Was told that unglued latex layers were not good for adjustable beds becuase the layers could creep down. Is this true?
If the layers are inside a suitable tight zip cover then in general no. If they do happen to “creep” over time (and latex is sticky so the layers don’t tend to slide over each other) then it’s an easy matter to zip open the cover and “wave” them back into position.
If you have a finished mattress that can’t be zipped open then it would probably be “safer” to glue the layers because you wouldn’t be able to access the layers if they do happen to shift over time.