As far as I know, the only cruiseline that currently has a "topless" sunbathing deck is Carnival. They will be implementing them on some Celebrity ships, but not sure if that has started or not, but haven't heard of one on any Costa ships, sorry. Unless there is some new information, I'd pack some tops :-)
Does anyone know the rules for who can be on the topless deck? Say I'm up there and my husband wants to come ask me a question, or tan himself - would it be ok for him to be up there with me? Of course he wouldnt' go up there alone, he wouldn't know what to do with himself and would be terribly embarassed.
I was on the Carnival ship Paradise and I went up there with my wife with no problem. There was a sign stating the rules on the door going up to the top deck. It said something to the affect of, No loitering or cameras. Hope this helps.