For Rosiebee, you've had lots of good advice on here, and there's LOADS more - on all cruise queries -- on sites like Cruise co uk, Cruise Critic, and more similar forums. As on here, others have done your planned trip, or very similar.
The advice re ship's tours does surprise some folk, do all you can to avoid them, as invariably you can do better on your own, OR there are cheaper (& very likely better) alternatives that you can pre-book via the i'net. The exception would be ports with lousy public transport, or the likes of Greece with a tricky alphabet, or the luxury cruise lines that include your tours (as you've paid for them with your fare!).
An excellent cruise (& airline) booker that we used several times is IGLU, who can help your plans if needed.