We did quite a bit of snorkel/kayak in Xcalak. You do not need a bouy, a long teather is sufficient to keep the kayak near at hand. Also it works best with a wide sit-on-top style kayak. For two of you a Malibu II by Ocean Kayak would work well.(It is the widest of the tandems at 33") Any other S-I-T Kayak wider than 32" is good. Practice in and out near shore, you will find that flippers make it easier to get up into the kayak. And if your partner is more adapt at getting in, they can always help steady the kayak too.

But in all things if you are going out as a pair alone let someone know where and your anticipated time back.