Not quite sure what you mean if you are taking your own wheel chair they can accomodate you.Also I had an accident whilst on a Costa cruise and was taken by wheel chair from the ship However I feel that you would need to speak to them and arrange it as they may have several people wanting wheel chairs.There are special cabins for the handicapped and I think every ship has to have them also in a variety of catergorie.
Not sailed on Costa but most cruise ships have a limited number of wheelchairs available. Always best to take one of your own.
Costa Romantica does have wheelchairs but they are only available for use when you book one of their tours. It is usually cheaper to book tours locally or take a taxi.