If it were me, I would book my own air. You will almost certainly obtain less expensive air. In doing so, transfers can still be added to your reservation, if you need them. I know it is nice to have the convenience of air/cruise all in one shot, but nine times out of ten, the cruiseline's air is going to cost you more.
Usually, in the Fall, airlines offer savings to Europe for great rates. If you are flexible, these fares can save you hundreds. Last year, I flew from Miami to Paris for less than it was to visit my son in Minneapolis. No lie.