Hope this isn't too late to help you, but it may help others, anyway. The following link gives info (and pictures) called Walt Disney World at Large, regarding rides and the types of seats - low bar, high bar, bench, etc, and lots of comments from people who have been to WDW.
I weigh more than you and went in May - I had no problems at all. There were lots of big people there having fun and I know you will, too.
Anyway here is the link:
www.wdwig.com/ridsiz.htm
After you read that part, click on the main page and find out what all is going on at Disney, plus lots of hints and comments.
Have a good time!!
Jana