When we set ours up, we set up a personal rep, a guardian, and a trustee, as our children are minors. One will settle the estate, one will take care of the kids, and the other will take care of seeing that the money is given to the kids for things like education, a wedding dress, etc., if something unexpectedly happened to us.
Your child's father could be the guardian of your son without touching any of the money. There are banks that can handle the trust part, however, they probably don't know your son that well. Do you have any close friends that might know your son well enough, or someone at church, who you would trust to manage the money? if something were to happen.
I would call around to see what attorneys charge for setting up a trust in a will, or maybe get a recommendation from someone. It really should not be that much.