Hi, Alison!
Congratulations on your upcoming cruise aboard the beautiful Disney Wonder to Alaska! I bet you are loving that the ship will be in your "backyard" very soon.
On Disney ships, the water in the pools and water slides are adjusted when outside temperatures are colder. Therefore, during the day, you may wish to take a swim...especially in port on Embarkation Day. Yet, when the sun is not up, you may find it more cozy to tuck indoors out of the wind or perhaps sink into one of the hot tubs. Of course, you'll definitely want to pack your swimsuit for the pools, hot tubs and the spa. I'll be taking this cruise the following month, and I plan on swimming at some point, too.
As far as requesting/paying for an upgrade, you may ask once you arrive at the port terminal on Embarkation Day. You will need to arrive at the port as early as possible and ask if any discounted upgrades are available. If they are, they will be sold on a first-come, first-served basis. You may be able to save much over the regular rates by purchasing your upgrade at the port. I do not know of any way to purchase an upgrade with any airline's frequent flyer program.
You are going to love sailing with Disney and wonder why you haven't taken a Disney Cruise Line vacation before now. Remember to pack one formal outfit, one semi-formal and lots of comfy layers for the sight-seeing you'll do in the ports. Oh, yes...and I hear that rain jackets are a must. Let me know how it goes!
Have a wonderful day and a magical vacation. Bon voyage!
Andi