Why not "ovviamente ti penso"?
why te and not ti? I thought ti was the indirect object, 2nd person singular
Here it's not an indirect object, but the object of the pronoun "a." "Te" is the right form to use after pronouns.
"a" is not a pronoun - it's a preposition. So after a preposition, you use te and me?
Yup. "A" is a preposition and it is followed by "te", "me", "lui", "leit", etc.
Parliamo di mamme [...]" should de accepted as well.