can a grantor also be the beneficiary of an irrevocable trust?

Yes, a grantor can be the beneficiary of an irrevocable trust.   I think that your instinct to safeguard the house from sale or mortgage is a good one, but I don't think that an irrevocable trust will get you where you want to be.   An irrevocable trust just means that the trust cannot be terminated or modified.  Putting the house in an irrevocable trust probably woud not prevent your son from selling or mortgage the house; the trust could just sell the house.  I suppose that you could have specific language in the trust that the house cannot be sold or mortgaged for a certain period but I'm not sure that would work given that your son is the only beneficiary of the trust.   To restrict what can happen with the house, my thinking is that you would need to transfer ownership of the house from him or put some sort of restriction on his rights of ownership.  For instance, you could have him grant you a life estate or life lease, which would give you the legal right to live in the house or rent the house for your lifetime.  Any sale or mortgage would be subject to this restriction so very unlikely.  Or he could transfer some or part of the ownership of the house to you; if you owned all or part of the house (as a tenant in common, not a joint tenant) he would not be able to sell or mortgage without your agreement.  If he transfers the house to you, you could leave it to him in your Will or even put it in a trust that benefits you while you are alive but goes to him when you die.  Any of these would be recorded in the Registry of Deeds and so available to any bank or buyer.  You could sign an agreement with him that you will pay off his mortgage in exchange for his promise not to sell or mortgage, but this is not as desirable because it would not prevent him from selling or mortgaging, it just would enable you to sue him if he did so.