This is our first year like this too. DS 21 is going with a friend mid September for a mini trip. That is a more hot/humid time than I would prefer (I'm not going though), but if you are used to July/Aug it would most likely be similar to that, but lower crowds. I was blown away at the inexpensive airfares they were able to get (including baggage and fees just $79 pp to fly down direct, and $84 pp to fly back - at their preferred times too). This is about 1/2 what we normally have to pay. I know on their MK day, the crowd level prediction is 3 our to 10, pretty nice. They were able to get a good deal on their accommodations too -- it's definitely low season. This is probably the least expensive and lowest crowd wise time to go.
And then in November, my mom and dad said they had a condo for two weeks in Orlando and dad said come on down and even sent me a check for airfare and tickets, so how could I say no -- twist my little finger. DH isn't all that fond of the parks/Orlando and isn't going, but DS 21 and I will go down for a mini trip for a long November weekend then the 10th - 14th. We were in Orlando last November when DH had a seminar at Universal. It was still a little humid I thought, but crowds were definitely more moderate than the spring break time we have done so often when we were tied to the school schedule. I didn't like the weather as much as spring break, but crowds just have gotten really heavy then I think, so don't really see us going there then with no tie to the school schedule.
It's been a long time since I went in May -- back when DS was 3, but it really was a lovely time I thought. So I think you are on the right track there.
Anything not during school breaks is really going to be a nice change from a crowd standpoint.