Protech and some others do take out small groups, from 2-6 people.

Hol Chan makes a good first dive. Shark Ray Alley is a snorkel-only place where you can play with nurse sharks and sting rays, and is a common second stop on the Hol Chan trip. Your husband can snorkel at Hol Chan while you dive. It's a local trip and you don't need to leave before 9am!

The Blue Hole is a good dive "if you like that sort of thing", and the other two dives in the day trip are world class open ocean wall dives. Your husband can snorkel at all three, though it's an expensive day out for snorkelling. For this trip you typically leave your hotel at 5:30am.