Severance offer, what should I ask for? - 18 weeks in

I was offered 11 weeks of severance after 11 years as a hotel front-desk agent, and I have a few days to sign. This is my first time dealing with any of this. There is a non-disparagement clause. 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.