If you don't want to fly, why don't you take the ferry over to Liverpool. Fred Olsen are doing a cruise (on the Black Prince I think ) departing from Liverpool ( and back ) on 20th Dec for 16 nights going to the Canaries ( It'll be far warmer than the med at that time of year anyway ). This website shows Oceanview Cabins available. From all accounts it appears that Liverpool Port is not the most sophisticated or scenic port to embark on a cruise, but then hey-ho you can't get everything!.
I think your only hope is Dublin Airport & fly to a port where a Med cruise is sailing from. I am not aware of Med cruises ever departing from Dublin. Regards.
My husband is forbidden to fly we would like a cruise next year from dublin.