I started a new position 6 months ago with a manager who is very reasonable and easy to work with. Unfortunately, that's about all that has worked out. I think my boss and I are on the same page that I am not a good fit for the company, the department, and the team.
Recently, I started looking elsewhere and I have been getting a high response rate (30% of applications get a callback), so I plan to leave soon once I find something better. My current role was open for over a year before I was hired, and there is a huge backlog of work (the previous employee who had my job left after 6 months too), so I have been thinking about negotiating with my boss a mutual parting with an extended notice period of 1-2 months rather than the required 2 weeks. I want to do this in order to preserve the reference despite leaving after just 6 months. I am less concerned about the long-term impact because my previous stays have been multiple years per position.
I'm thinking I would negotiate in early November to leave in mid-December - about 5 or 6 weeks notice. How should I approach this subject of a mutual parting with an extended notice period with my boss?