We went the last week of Jan 2020. LOVED it. The crowds were manageable and the weather was so much better than June. We aren't pool people, so we didn't miss that at all. It was relaxing, we rode everything we wanted except FOP and 7DMT, and we were out of the parks by dinner. We stayed offsite, so we took advantage of the less expensive options outside the parks at night.
We had such a great time that dh, who really, really doesn't like it when I suggest Orlando theme parks for vacation, volunteered to come back Jan 2021 to do Universal and "that after dark thing you did with your sister in August" (MK DAH event). So, that is already booked and we are not cancelling it. Well, except that there is no DAH this year, so we'll just do one day at MK instead.
We wore jeans / jeggings every day; paired with layers. Highs ranged from upper 60s to upper 70s, and lows were mostly mid-50s. I only wore a sweatshirt one day, though I did wear a jacket over a french terry hoodie over a t-shirt the morning we hit HS at 6am in the dark and mid 40s. By lunchtime, the jacket was in the bag. Dh wore short sleeves most of the week, and told me it was the first time he'd been to Orlando that he didn't sweat himself to death. We drove, so we were able to overpack. We're flying this time, so I will have to be more strategic with packing, but do plan for 40s to 80s, and bring light layers and a park bag that can hold the things you take off.