I would like to have my domestic partner (legal) to make decisions for me
Should I stroke out or something equally as devastating. I would like her
To make medical as well as financial decisions even though I have a will
And someone else as executor. Do I have to go to a lawyer for this?
I live in New York

Health Care Proxy - Appointing Your Health Care Agent in New York State (http://www.health.state.ny.us/professionals/patients/health_care_proxy/intro.htm)

That will take care of the health care issues. You can then create a limited power attorney that will go into affect only while you are not competent to make your own decisions.

It answers part of it. I was asking if I need to go and see a lawyer for this or can I get the forms online.

You don't need an attorney, though it would be advisable to consult one.