Aldora Divers is what you're looking for. Advanced divers once with them aren't going anywhere else cause you'll be in their special little 'club'. They specialize in putting advanced divers with each other on small boats with groups smaller than typical size for Cozumel and then going after the advanced sites without newbies on board to ruin it for everyone else. The marine park rules are 1 dive master to every 8 divers, Aldora has their own rules which are 1 dive master to 6 divers. They are going to silently check you out on your first day and place you with an appropriate group for the rest of your trip. Once you get onto that advanced boat you'll be in heaven. Steel 120s of course are the norm with them and they are all about bottom time. One of the few outfits on the island with enough boats to segregate divers, one of the few outfits on the island with the foresight and financial ability to have their own fill station including nitrox. Only outfit on the island that can dive the east side of the island and they are currently the only operation opening up new dive sites north of the island. They won't be the cheapest, but you get what you pay for.