You're in luck. I was just there in October. Dove with Rocket Frog dive shop in Playa Del Coco / Playa Hermosa. Had an absolute blast with them. Diving was good, hotel were we at had great food and the staff was awesome. And i went to check out the other dive shops while we were there. Rocket Frog isn't the type of shop that's got a buncha gear to sell, but that's the nice thing about it. They focused solely on the diving aspect. We also did the ziplining, horseback riding, white water rafting, and rock climbing excursion with Bill Beards.
Had a great time, just make sure if you pay them to do the photos, that you take a spare USB thumb drive and have the pics download to that. The CD they gave us at the excursion wasn't formatted right when we got back to the hotel. They made it right by putting it on a drive for us and delivered it to the hotel.
Rocket Frog Divers
Hotel Colono Beach Property, Guanacaste Province, Playas Del Coco, 50503, Costa Rica
+506 8562 3340
https://maps.app.goo.gl/KJ8Gn