My STBXAH and I talked it over and went through the "this time I'm really getting sober" dance a few times before I told him I was done. Then we discussed trying to have an "amicable divorce" and work together to make things as smooth and inexpensive as possible. We did the paperwork together, in a mediator's office.
I would recommend keeping the emphasis on the positive, for example letting her know what you say above about wanting to make the settlement go as smooth as possible.