The 4 island trip sounds too hectic. Which trip will give a pleasant experience, given the temperatures and hoping for calm sea?

 

PP on the cusps of high/low season.

It really depends on what kind of an experience you're looking for.

I've done a few trips to different islands over the years, so there is plenty of choice, Similan that was a long day and was so crowded I wouldn't go again, another time I went to Rok island at that time was really deserted and we had a buffet lunch on the beach, or you could stay local go to Rawai beach and get a long tail boat to Coral island,

 

Go to this web site see many trips, https://bit.ly/3GQiYUT 

In truth, most of the island beaches in Phang Nga Bay are similar, you could be on any one of them or indeed still on Phuket.   For an overall experience, I would recommend the sea canoe excursions.   The vessels are large and quite slow, and sheltered from any adverse weather.   Leaving from the north, particularly from Laem Sai pier, means a relatively short journey time and the best scenery that Phang Nga Bay has to offer.   There will be food and drinks onboard, inclusive of the tour price (probably beer extra if you want it).   You won't actually paddle the canoe yourself, there will be a local guide doing that, and each canoe can carry three people (guide included).   Overall, much better than being bounced around in an open speedboat.

Koh Rong in Cambodia.  Beautiful, just paradise.

 

Or if you like something more "Themed", look up Phu Quoc in Vietnam (Also by Cambodia)

Shraksy,

Thanks for you suggestions which are off the beaten track