Please do my thinking for me :)

[Subcooled]

My SO and I have ~10 days in early November and I'm thinking of the Yucatan. We'd like to do [...] a visit to Tulum and/or Chichen Itza...

Or rent a car and drive to Calakmul and Rio Bec Dreams. It was an unforgettable experience. I don't know how safe it is today. 20 years ago there was a military roadblock and me not speaking spanish... Security advice is not included.

In Tulum there are many cenotes, e.g. Hilarios well (snorkeling): https://www.tripadvisor.com/Attract...s_Hilario_s_Well-Tulum_Yucatan_Peninsula.html

A little bit south of Tulum there's also this nature reserve: LA RESERVA DE LA BIOSFERA SIAN KA´AN, PRINCIPAL RESERVORIO DE CARBONO

can anyone suggest an itinerary that would be easy to put together?

• Chichen Itza + dry cave visit + swimming in a cenote (e.g. Dzitnup or many others) is a daytrip. So, maybe you could include a cenote dive to the Chichen Itza trip if you start early and plan well(?). I have not been diving in cenotes.
• A no hurry travel to Calakmul area and back took three days (no diving there).

the only issue might be needing an AOW cert for the cenotes(?)

I found this: Cenote Diving Rules, Requirements & 3 Important Safety Tips!