I did the "tourist" thing with a day boat to the same area on July 20th - seas were too rough to enjoy the trip, thrown from bench to floor more than once so I just stayed on the floor.
Whale Sharks were just as amazing as you experienced, but my day was cut short since everyone on the boat (except me) was seasick - I think I got 5 times with the whale sharks, which was amazing, but annoying since I wanted the entire day.
Too many whale sharks to count, too many boats to count and not one manta in sight.
Wet suits - Bare Progressive Stretch (3mm, 7mm 2pc) - would buy again - great suits, easy to don, keeps you warm because it hugs you with the extra stretch.
Dry suits - Abyss (Canadian made) Compressed neoprene suit (7mm compressed to 4mm) - lasted for 300 dives and then the zipper went bad. Happy with the suit, but now that I have a shell suit I'm not going back to neoprene.
Dry suit - Otter (UK made) Britannic front entry - love the latex seals, love the front entry, love the cargo pockets that are standard (no extra cost), love the sock boots!! Would buy another in an instant!!