I looked into that thing you asked about. It turns out most traders don't build a sickbay into their ship because they want to save on weight and/or they don't anticipate being in many situations where they'll be shot. Maybe you'll feel the same way. But if you change your mind, the outfitting is pretty standard; it's two displacement tons, and will cost Cr200,000. If I understand your situation correctly, your mysterious benefactor will take care of that.
A sickbay will give you a dedicated recuperation platform, a place to store medical supplies similar to a ship's locker, as well as a place to conduct surgery if the need arises. So think about it; it might come in handy.
I should have known you'd fly off and have your own adventure someday. Please be safe.