Diving - Greek islands

I searched the forum and found some 5-year old threads on this, so figured I'd start fresh. My teen son obtained his advanced open water dive certification this past summer and was interested in trying to dive in the Med next summer for a change of pace while we are on our cruise. (Sad story and a bit of a deviation - he's gone to the same sailing/dive camp in Tortola for two years now, and was there in mid-August. Just a few weeks later, it's decimated. The fleet of boats they used are largely sunk, missing, or damaged, with just a few emerging unscathed. Fortunately the permanent staff is all safe and sound. Still - it is so fresh in his mind that the pictures we are seeing of Tortola just astonish him. Now - back to your regularly scheduled program.....)

Anyhow - he wants to go back to Tortola if it's ready next summer, but with a cruise out of Venice stopping in Mykonos, Corfu, and Santorini, we're thinking a day at the beach or snorkeling for us, with him doing a boat dive to see something new would be a great way to remember an island. We want to "tour" Santorini, so leaning towards Mykonos or Corfu. Does anyone have any experience or recommendations?

I found one company - W-Diving - that appears to be right on Kalafatis Beach, but having trouble finding much else, so thought I'd ask this wide group! Ideally we'd find a reputable dive shop that is conveniently located to a beach that the rest of us could enjoy while he's doing his thing.

Thanks!