There is something I don't get: if currentitem points to the item itself and not to the position in the list, you cannot do a currentitem + 1 as the value of currentitem has nothing to do with the position.

The canonical way of doing what you want, is indeed going through the ordered list until you find the item and then going one item further to find the next. As you will not have lists with scores of thousands of items, the overhead seems small.