I am not from Singapore but here are threads that might help:
Jeweller recommendations in Hong Kong/Singapore
Calling out to PSers based in this side of the world! I've been a long time reader of this forum, and have poured over many threads about the amazing jewellers based in North America. As amazing as they seem, however, I would appreciate a way to get the quality from talented local jewellers...www.pricescope.com
I think I remember seeing someone suggest Madly Gems: https://madlygems.com/