Volunteering with blanket L1, COS needed?


I have blanket L1 for 3 years, and currently I’m working in the US. I have temporary contract 'til end of this year. After that I wan’t to stay in the US as a volunteer. My fiancée wan’t to join me, and I’ll marry her at December outside of the US. At December she can get an L2 visa. I guess after we come back to US we can request a COS. My question is that what kind of visa do we need?