Our standard is 4 items per person: a fleece jacket, a windbreaker with a hood, a pr. of thin silk long underwear, and light gloves. We find that layering these is normally sufficient as long as you have long trousers and some closed-toe shoes for nippy days.
PS: Do remember that Orlando is not Miami; it can and sometimes does experience hard freezes, and on a WDW trip you are going to be in windy situations outdoors at night. Thus the thin long underwear: normally I wouldn't need that at home, but when it is 30F outside and you are sitting on metal grandstands, your legs can get cold even with long trousers.
Minnesotan conditioning situations aside ;-), it is normal in winter for nighttime temps in Central Florida to be 30-40 degrees colder than daytime temps. One day last week the 6 am temp was 37F, by 9 am it was 62F, at noon it was 77F, and at 10 pm it was 40F. The wind that day varied from 7-23 mph as a front moved through.
FWIW, at this time of year the parks all sell fleece blankets for those people who pack nothing but shorts and tees with them. One size fits all, I guess. I saw several people getting on the bus in the morning wrapped up in those blankets.