In my limited experience (1-2 trips a year for the past 11 years or so), I think one is most likely to experience stronger, even bizarre currents in the Spring. But at all times of the year it is variable, with one day or one dive site being strong and the next not so much. Cozumel is usually a drift dive location and one has to expect current. If you would like Caribbean boat diving with less current I would suggest perhaps the Caymans and the Virgin islands as possible good choices with likelihood of good visibility. Bonaire and Curacao also rarely have much current but are primarily shore diving locations, although you can do boat diving if you prefer. Roatan might also be a good choice for you, if shore diving is acceptable. Dont' go to Tobago.
I am unsure on this and perhaps those with more experience can confirm or correct me, but I feel like the mid-late summer is probably the "calmest" season from a current standpoint, unless there is a tropical storm or hurricane somewhere in the area. That is just a vague feeling.
Good luck to you and your wife in finding the diving you like. It is out there.