Just got back from Bali yesterday and thank you all for the advice about the cold. It helped as waters was indeed cold.
On the first day about 930am at Manta point on 23rd Aug, water temp was 20 degrees C. But luckily a Manta made up for it. I was in a rash guard, a 5mm suit and a hood (through your advice). Yet I was stilling feeling cold. The second and third dives were at Crystal Bay. Water was although slighly warmer at 22 degrees, suffered even more at the expense of no sightings of Mola.
On the second day, headed back to Crystal Bay again to fight the cold on the first dive. This time, temp was 20-21 deg C again. However, we got lucky and spotted 3 Molas (I was told). I only saw 2 thou as the 3rd was dark/black thus probably why I missed it.
On the last day on 27th Aug, we visited both Crystal Bay and Manta Point. After 4 days of diving (3 in the cold), one would have though I would have gotten use to it. But hell no! Crstal Bay had temp of 21 deg C while Manta point was a stunningly low 19 deg C. Worth the cold as spotted 2 Molas at Crystal Bay and 3 Mantas at Manta Point (above 10m water dept). On the way back from Manta Point to SD Reef. We were blessed with half a Mola above water.
Overall, the trip was good and fulfilling. Nevertheless, it was tiring and straineous trip because of having to (1) fight strong currents, (2) braving the long and choppy seas rides on a speedboat (at certain times was feeling seasick); and (3) enduring the cold. Would I do it again, not in the next 2-3 years.
Yes, I booked the trip through a local dive operator (Bali Scuba) as per recommended. Would definitely head back there with them the next time around.