Dan
Contributor
Not sure if you made your plans yet...
My wife and I spent a month in Bali last December and dove quite a bit while there on Bali and the Gili Islands. Of all the diving we did, by far the dives off Nusa Lembongan and Nusa Penida were the best. It was December so we missed Mola Mola season, but you may have some luck in November. We were told the week before we were there, there was a sighting. Water on the Nusa's were a little chillier, but had no trouble 3mm wetsuits. There are some decent currents off the Nusa's, something to keep in mind.
We used World Diving and highly recommend them. Also looked at Dive Concepts, but didn't get a good vibe from them. Then saw their boats out in the water and they had way too many divers on the boat for my comfort. Your mileage may vary.
If you want to see Mola Mola, come during July-September. I’ve dove in Bali almost every year since 2007, at different month of the year, April-December. I have zero luck of seeing Mola Mola after September and before July. August during full moon or new moon was the best time to find them. I saw 9 of them in August, 2014. I was in Manta Point & Blue Corner on September 20, 2019 and saw these guys: