Should I negotiate my severance? - 10 months and counting

I was offered 9 weeks of severance after 9 years as a recruiter, and I have a few days to sign. It has been a long 12 weeks. I do not want to leave money on the table. Did anyone negotiate and succeed?

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.

I asked for two more weeks and a neutral reference. They agreed to the reference and added a week.