Hi Jessica,
Glad to hear you're planning another trip to Disney World!!!
You will still be able to obtain a Guest Assistance Card (GAC) for your son without any special documentation being required. I do recommend Guests bring any medical records regarding any medical conditions. You won't need them for the GAC but its good to have them in your room in case of an emergency.
I am not sure what other types of assistance you may require for your son. Disney does offer several types of assistive devices if he needs one. Click
here to see a list of the types of visual assistive devices currently provided and
here to see a list of hearing assistive devices.
I also recommend that your son have some sort of identification on in the rare event that you become separated from him. This is especially important if he is non-verbal.
If he has some small comfort items that can help calm him if he becomes upset, bring those with you as well. These may come in handy especially in the theme parks.
If your son is easily agitated in unfamiliar situations, you can request a room that may be a little more secluded. I like being on the ground floor in a corner room when possible. This may not even be an issue for you. If you decide you could benefit from this, please keep in mind that special room requests are just that - requests and they are not guaranteed. If you explain any special needs you have, the Cast Members always do a great job of accommodating them when possible.
Please let me know if you have any other questions. I am super happy to assist you make this a wonderful and stress free vacation for you and your son.
Wishing you many magical memories :-) Allison