Welcome aboard, Rosalba! My family has traveled on Disney's cruise ships in January and February the past couple of years and have had amazing weather each time.
Now, we are coming from chilly Ohio, so if there is not snow on the ground in the winter, we're happy! But, I see you're from Buenos Aires, so it might not feel quite as warm to you as it does to us in the winter months. A few weeks before you sail, be sure to check the weather forecast as that will give you a better indication of what to pack, but do expect upper 70's to low 80's for the most part.
At sea and during the evenings on deck the weather is cooler and windier, so pack a light jacket. We love that Disney provides blankets on the pool deck area for guest use on the cooler evenings. It's so nice to snuggle up in a lounge chair and look out at the ocean.
First time Disney Cruise Line guests will be able to begin booking any extras like Port Adventures 75 days prior to sailing, so take this time until then to check out which
Port Adventures look good to you. If you haven't been to Atlantis in Nassau, it's surely something to experience and there are many different adventures that will take you there. On Castaway Cay, many fun events and activities are included like crab races, character dance parties and more. There are official Port Adventures that you can book as well, and snorkeling gear and bikes can be rented either beforehand or once on the island. If you don't see a Port Adventure on Castaway Cay that you must try, don't worry! You'll be so busy with everything else that is offered that you won't miss it!
Have fun as you continue to plan, Rosalba! I'm happy to help with any additional questions you might have!