The only thing holding you back from using a queen size mattress on a full double bed is the length of the bedframe. It is easy for use to extend the side rails to accommodate a queen size mattress. The other consideration is esthetic. Because a queen mattress is 60" wide, the mattress would overhang the side rails by 3" on each side. It's your call as to whether this look is for you.
So, if you fall in love with one of our full double sized bedframes, but need it to fit a queen size mattress, it's not a problem! Here's a link to more pictures of this bed http://www.antiquecastironbeds.com/double-beds/delightful-double-d582s