You need to make sure the fields you wish to use in your link column are present in your interactive report. You can do this in addition to your derived fields, and set the Display Type of the individual fields to Hidden should you wish to.
But the more straightforward solution is as Jeffery Kemp commented, just to use the primary key in your link column and then pull from the database using the primary key when loading your form.
If you create a new page, choose Form, and the "Form on a Table with Report" option, ApEx will do all the hard work for you.