I do not know if you have your heart set on Tulum, but as an alternative, right up the road is Puerto Morelos. It is often overlooked for more flamboyant destinations like Cancun and Playa.
Bret Neilson runs a nice dive shop there with his wife, who also is also manager of several properties. I have stayed there twice and my daughter a third time when she did her DM internship. The town is small, friendly, safe and quiet, with a few local bars, markets, shops and resturants. The town is still focused around its town square or Plaza. And English is no problem if you are not fluent in Shanish. When I was last there, there was only one large resort, but it was about a mile down the beach and you hardly ever saw anyone from it. I have never seen the drug peddlers there like I have in Cancun. I have been just amazed that the crowds have not found Puerto Morelos yet. It is about a 30 minute drive down to Tulum and about a 20 minute drive up to Cancun's beaches. The reef is nice; not Cozumel nice, but Mainland nice. :grinbandit:
Here is Bret's website and you can email him for more info if this appeals to you.
Welcome to Dive in Puerto Morelos
Have a good stay where ever it leads you.
~Michael~