What team structures have you explored, and which do you recommend?

Two dimensions to think about: product and operational. 

PMMs need to be aligned to persona solutions. If the product set only has one key buyer there may be opportunities to break down by user personas or level two buyers. 

If that's still challenging I would suggest thinking about operational or functional alignment. 

For example: 

- Messaging PMM (FCD, website, PR)

- Technical PMM (demos builds, videos, release marketing)

- Events PMM

- Enablement/GTM PMM (leads sales enablement strategy or supports GTM for a specific segment or industry)

PMM team structure nirvana is having a mixture of all of the above. At the end of the day, it's largely driven by the needs of the business.