Curacao Trip Report with SB Surge Jan. 2019 Fun, there are kids around but you can minimize that by what time of year you go.
Cozumel has a number of A.I. resorts. I have not stayed at them. I think
Secrets Aura Cozumel is adults only. I don't know what their dive op. is, if they have one, but in Cozumel some divers choose to dive with an off-site op., even if the resort they stay at has one.
It seems your focus is on quality diving, and from what I've read, with Sandals the resort rather than the diving tends to be the main feature, so I didn't get into those. Sandals struck me as pricy when I explored it in the past, though I don't drink alcohol and that's included.
Richard.