You can try approaching Livingseas where you can do your confine open water in Singapore then the actual open water dives in Bali (since they have both Singapore and Bali operations).
Bali has a variety of dive sites suited for different levels of diving. Jepun site located in Padang Bai is ideal for beginners as it is in a bay area.
When I was there in mid November, the water temperature can go as low as 19 degrees C!
Hope this helps!