Hi Kimberly,
My family has visited Walt Disney World many times in July. We found mid July to be crowded, but not crazy. We were able to enjoy the parks without feeling too overwhelmed. It is hot. I think you are smart to be thinking of ways to give your son (and yourself) a break.
My first suggestion is to find a quieter air-conditioned attraction, like the Hall of Presidents at the Magic Kingdom, to enjoy and possibly give your son a chance to nap. Even though it's a little loud, "it's a small world" put my son to sleep when he was small! Epcot has it's share of dark, quieter attractions as well. Ellen's Energy Adventure and the Gran Fiesta Tour Starring The Three Caballeros can be nice for a few cool moments out of the sun.
My second suggestion is to check out the fantastic
Baby Care Centers located at the parks. They are quiet and tucked away from crowds. There are changing stations and rocking chairs for resting a bit.
I hope this has helped. Please let me know if you have any other vacation planning questions. Wishing you and your family a magical vacation,
Amy H.