So after our first few stops (Kuala Lumpur, Brunei for the day, Kota Kinabalu, and Borneo Rainforest Lodge), for our last few days of trip, I think we are going to go to the Six Senses Yao Noi in Thailand. We can get to Phuket by 10AM the day after leaving Borneo Rainforest Lodge, and there are lots of direct flights from Phuket to Singapore, where we will be flying back home from.

That you all for your input - the St. Regis Langkawi just doesn't seem good for August, the Eastern side of the Malay peninsula would take longer to get to and from, there are not high-enough quality resorts around Borneo, and my Singapore friend did not recommend the Desaru area, so Yao Noi seems to be the best option!