There are many important issues here which really should be considered before proceeding.
#1: will you be on title for the home or just on the note? There's a big difference.
#2:Does your husband know about this? if you are on the deed, your husband will need to sign a quit claim deed.
#3 who will be making the monthly payments? will you be charging your son rent and paying the monthly loan payments yourself?
#4 who will be making the down payment? If you, will it come out of a joint account with your husband or from your own separate funds? There would be the issue of community property to be considered.
#5 Will you make or will he be paying the monthly loan payments directly to the bank? Please know that if the payments are not made, you would be fully liable even if you are only a part owner or not on title at all.
#6: talk to an estate planning attorney regarding your estate plan. At death any debts are due to be paid.
I'd suggest you consult with an attorney as there could be some real consequences for doing this. You might considering buying the home in a Trust.