I would switch out the Rennie boots for a pair of knee-high combat boots, or wear long trousers with steel-toe shoes... and trade out the leather jerkin for a shirt, braces, and vest like this:

the pattern is Simplicity #5037, it's out of print but you can still order it from the Simplicity.com site. #2895 is still in stores, it lacks the hat and braces but has a similar vest & shirt, along with a frock coat which might also be a good look-- though you'd have to do some hardcore tailoring to fit a suit collar around the fursuit's neck. You could even enlarge the cap pattern in the first outfit, wear it over the head, and cut holes for your antlers.
biggrin (Sorry for rambling about sewing patterns-- Your costume is well-made, so I'm assuming you sew, or know someone who does.)
I agree with the previous poster about adding a monocle- your suit's head has spectacular eyes, and a monocle would really bring that out. It would be pretty simple-- they sell brass rings of all sizes at craft stores, just atttatch a length of chain to the side and stitch the ring to one eye, loosely enough so you can remove it to go back to the medieval look
smile Or, make a pair of HUGE goggles.
Since your character's a courier, maybe add a rocket-pack? A holster and a ray gun? The possibilities are endless!
biggrin