I would also suggest Liverpool to Palma with EasyJet, as Liverpool is a small airport without the hassle of London or Manchester.
Just so easy at Liverpool and Belfast is just a short hop across the water from Liverpool.
Looking back on my previous bookings Winter EasyJet flights are released in July from Liverpool to Palma. Usually about £50 - £70 per person or much much less if you are very very quick
Usually only one flight out each day in Winter though and its early in previous years.
Not Sure if April 10 might be into Summer schedule ( more flight times), and those flights are released about November in previous years.
These dates may change this year with the Recession and low amount of bookings and low euro rate etc.
I guess flights will be released earlier than previous years to get some money in
April 10th is a Friday in 2009, so you have a good chance of bagging some bargains, as nearly everyone goes for a Saturday flight.
So make sure you are signed up to Easyjet emails for the various airports you are interested in.
Will not be long before that EasyJet email arrives and panic booking will begin before the price goes up..
edited to add:
If you can get a direct flight from Belfast thats the best way of course ! ( as long as its cheap)
Mark.