On deck you might need to bring a sweater (a fleece zipup would be perfect) as it does get chilly but indoors you s/b fine with whatever.
The indoor pools were heated and usually crowded (school's out!) but worth it. The outdoor pools never opened on my cruise as it was just too chilly (July). The hotubs were the place to be !!!! We spent a lot of time in them
We didn't wear shorts at all on the cruise but that was mostly b/c our excursions were not short friendly. However in Vancouver, we wore shorts and it was quite warm so bring an assortment and be prepared to wear items more than once. You'll be fine.
Have a great cruise. You are going to love Alaska!