The diving in Belize is spread around a big area so one apartment isn’t going to work and I wouldn’t rent a place in Belize City on a bet.
For a big selection of dive ops and food you might want to look at West End, Roatan
Utila is another place with a big selection of dive ops and food all within walking distance but getting there can be a problem. For travel arangements you might want to contact Roatan Charters