Selecting Multiple Categories

[ Moderator note: moved to Fixing WordPress. ]

Hi
Would it be possible to select 2 or more categories, i have a pillowcase site and i want the possibility for the visitors that they can select size and niche for instance: dog and 18*18 inch

I have been searching for days and i haven’t seen any free or paid solution to this problem, is there anyone here that can point me in the right direction

Thanks

Dave