We just returned and as I had these same questions before our trip, I wanted to respond to a few threads to help other "Pooh-shaped" posters.
I am 5'3" and wear a size 26/28 pant (depending on material) and a 24/26 shirt, with most of my weight in hips and thighs. Small shoulders and upper body.
I was able to ride FJ the first day, when I wore a thin, parachute-type material capri pant. It was a tight fit, but once the ride began, everything shifted a bit and I didn't feel so squished. So psyched to be able to ride it!!

However, on our last day I tried the test seat (after 6 days of eating out, I wondered if I had gained, lol) and did not get it to latch - I think due to the jean capris I wore that day. I might have been able to fit on the ride itself if I had made more attempt to scoot all the way into the back of the seat, so that the thinner part of my thighs was near the latch, but I didn't want to take a chance I wouldn't fit.
Was not able to fit on the Hulk modified seat, the Dragon Challenge or Ripsaw Falls (this one was mostly due to having to get down into a log - I fit into the back seat, but was afraid I couldn't get the lap bar down or get back out of the ride at the end!), and didn't even try the seats at Rip Ride Rockit.
The lap belt on Bilge Rat Barges was a struggle, so the TM pointed out a seat with an extended belt and everything was fine there. I was able to ride Mummy, Simpsons, MIB, Spiderman and Flight of the Hippogriff (DD and I each rode in our own car, we asked and the TMs were happy to oblige).
Good luck, I hope you are able to ride most of the rides!
pigby, best of luck to your DH, I hope he makes it this year.
