You may find a standard flange towbar (with the two bolts) will very low profile when there is no towball installed. (you don’t need the towball if you get a bolt on rack)
If you still think it’ll be a shin basher, I think Witter do a ‘flange detachable’ rather than the normal swan neck style, but it does cost a bit more.
From what I’ve seen, the racks that clamp onto the ball can gouge the towball, ruining it for towing purposes.
Here you go: This car has a normal flanged towbar. The silver bump plate is only a few millimetres from the bumper, which means the towbar itself minus the towball and bump plate are as near as flush to the bumper. So the only protrusion you will have is whatever bike rack mounting hardware is left bolted to the towbar, and the electric plug although normally this can be bent back so it doesn’t stick out. The electric socket in the pic is the supplementary socket for a caravan which you won’t have, the black socket for the lights is on the other side and normally a few cm’s lower down, giving a bit more space to bend it back.