Should I negotiate my severance? after 6 years as a graphic designer

I was offered 6 weeks of severance after 6 years as a graphic designer, and I have a few days to sign. There are 6 people counting on me, so I am trying to be careful. There is a non-disparagement clause. Did anyone negotiate and succeed?

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