use a suitable linked list module, or there might be something similar under "sequence" in CPAN. this will help keep the design logic separate from implementation.
as per your clarification, you're interested in being able to follow sequences. An artificial contrivance such as text box co-ordinates will surely slow you down in implementation, not to mention horrible maintenance. the basic idea is of sequences or linked lists or such. if you use text box co-ordinates, they'll need to be re-computed for shapes following an insert.
all the best in your project