T.S.
I would just use the strollers they have available at Disney. Why buy and lug something along when you can just use what they already have available at the park? I think they also have wagons too, which could be a good option if he's able to walk at least part of the time.
And keep in mind, STROLLERS ARE NOT ALLOWED IN LINE, which is where you will be spending a fair amount of time (you park the stroller outside the entrance to almost every ride/attraction.) Disneyland involves a fair amount of walking but it also involves a huge amount of standing and waiting.