You would get the first (or second) round draft pick of the signing team, plus a pick in the supplemental round.
If the signing team is drafting in the top half of the first round (i.e. in the first 16 picks), you would get their second round pick. If they were drafting 17 or later, you would get their first round pick.
A couple of caveats: (1) if the signing team signs multiple type A's, then you might get their second, third or even fourth round pick; (2) if the FA doesn't get signed by the time draft lists are released, you don't get any compensation.