Beyond cardigans, we like sweatshirts that zip. Dark colored hoodies are great at WDW. (built in head cover if it really gets cold) I'm also a huge fan of fleece.
As other have said, it's not just the highs you have to think about, it's the lows, the amount of sun, and the amount of wind. We tend to stay out late at night in the parks. After dark, the wind can really pick up. I have more than one picture of us wearing four layers! If you are the kind of folks that stick more to daytime hours, you probably won't be out the low temps as much as us.
One packing 'trick' is to bring extra socks. An extra pair of socks only takes up a little room in your luggage, but warm feet go along ways towards keeping me happy. I don't mean just ankle socks...the under jeans option of cotton tights or thin thermals is also great, and again, they don't take up much room in luggage/day bag. Hats/gloves are also an easy luggage 'stash.'
Layers are wise. I like to bring a little of everything: tank tops, long sleeves, hooded sweatshirts, windbreaker. I'd rather be prepared than uncomfortable, without overpacking. Many times, I've been very happy to have a winter coat with me at WDW.
Epcot always feels the coldest to me. Partly because there's so much open space. To make matters worse, at night, most guests are over by the big lake (WS dinners/Illuminations), or on Test Track. On your AK day, conversely, you know you won't be out late. AK also has lots of wind protection.
Beyond that....during the holiday season at WDW, particularly an area like the Osbourne lights area, it's fun to adopt a 'winter holiday' look. (Think: Old Navy commercials) If you've got a took, it makes for a fun photo op, and it keeps your head warm!
There's no lack of opportunity to buy shirts and sweatshirts at WDW. They don't really sell jeans. Socks are hard to find. (been there, WDW charges a premium for socks and underwear...)
Still one more good thing to know...worst case scenario - there is a great outlet mall (actually two) located just off WDW property. They have lots of big names like Nike, Gap, Oshkosh, Levi's, etc. It's just across I-4.