good luck with your decision what ever you decide.
We had originally planned to go at the end of July when I'm 34 weeks - but my husband likely has business travel then so instead of cancelling altogther we rebooked for July 4th week when I'll be 30 weeks.
Originally in-laws were coming with us and we were going to stay at SSR. Now, it's just me, him and DS3. The trip is entirely for DS3 as a last trip before the sibling so he can ride the train and small world as much as he wants (he tells us what color train he wants and sings it's a small world all the time). We changed our booking to the poly and club level and I think it's the best decision we've made. my son's not a thrillride kid so we'll be able to take things really slow and if we only ride 2 rides, good enough. we go fairly often that rides are not a priority for me. I've asked my dr at each visit about the trip and she keeps telling me that i'm good to go. Since you know your own pregnancy history -- then you know what to expect.
(the 1st one was easy -- now if I had the history of a friend of mine who went into labor 10 weeks early, I wouldn't be considering this at all)
Good luck!