It's worth a shot, Liz.
Mediators are pretty good at pointing out the "wins" for both sides. It certainly seems a hell of a lot less aggravating than trying to negotiate with him yourself, and a lot cheaper than having a lawyer do it.
Maybe you want to propose an agreement to use mediation PROVIDED he agrees not to discuss/argue the issues EXCEPT at mediation. That might give you an out if he starts haranguing you at home. You can just smile and say, "Hm, make a note of that to bring up at mediation."