The pronoun ipse is not a third person pronoun. It can be used with the first or second person just as well. The closest English word I can think of is "-self" from which one can form "myself", "yourself", "himself", and others.
Reference to first or second (or third!) person can be left implicit. You can say ipse sentio ("I myself feel"), no need to say ego ipse sentio.
It is possible to use it together with ego or tu as well, and that gives more emphasis. It also proves unambiguously that the pronoun can go together with first and second persons. For a couple of examples, you can check uses of ego ipse and tu ipse in Cicero.