Do I need a elder law attorney?

I assume you are worried about inheritance. If you were considered a contributor for your son at this time your assets would already be disqualifying him from receiving SSI. You may put your assets in a special needs trust to shield them and provide for your son on your death.

Speak with a local attorney regarding a special needs trust and/or use of a testamentary supplemental needs trust as well.

It's a good idea to meet with an elder law attorney in your area. A special needs trust can be set up to put your money towards your son's care and special needs while not disqualifying him from Medicaid. Also, be sure to ask your local elder law attorney to discuss Medicaid estate recovery laws in your state. That may be what you're referring to when you said "Medicaid payback".