All cruises that originate in the US have to visit at least one non US port before coming back. For instance Alaskan cruises stop in Canada too, East coast cruises also stop in Canada, etc...I don't know if it a sure thing or not but I have heard that.
If you want Disney then go to them directly. You can find all kinds of inclusive cruises if you look for them. Often the cruise cost includes air fare.
Personally I have heard that Disney has the smallest rooms. But that is supposedly because they have so much to offer with the shows and amenities. They go to places like the Bahamas and stop a full day at their company owned island. There are a lot of activities on the island but they cost extra. Each thing you do off the ship is an extra charge so you need to make sure you have extra money stashed on a card so you can access anytime you need it if your room bill gets high.
I have no interest in going to a cruise ship's company island for a full day. I don't really want to go to Nassau either. I can't fine anything interesting about go to a straw market shopping.
When we were looking at going on a cruise we planned on driving to Florida or taking Amtrak. Then going on Royal Caribbean, I wanted to do the rock climbing wall and ice skate while traversing the ocean...lol.
If you google yahoo travel then click on cruises you can find all kinds of good ideas. The things I think about when planning this kind of trip are: Who is going, mom and dad? or the kids too? Is the primary goal to spend time in the water? seeing the world? playing/staying mostly on the ship and taking advantage of the numerous restaurants and show? or do you want to just spend time in Disney World? then get on the ship for a couple of days on a short trip.
Lots of things to consider for sure. Good luck planning your vacation.