Hi, toddlich.
I am planning a trip to either Holbox or La Paz in August and doing research as well.
I contacted Blue Angel dive shop in Cozumel and they recommended a Mawimbi Hotel.
Here is pretty informative website
http://www.holboxisland.com
From the conversation with the dive shop I got an impression that there is some sort of tourist war is going on between Cozumel dive shops and local people of Holbox. Locals understood the tourist value of whale sharks tours and don't want anybody else on their market
I might be wrong, but that's the impression I got.
Dive shop told me that they would organize a trip to Holbox but only if there are enough people interested.
You posted your question in March, did you gather any more information? I'd be glad if you could share it.
Cheers,
oceanrealm