I think many clinics in Bangkok can do beautiful double eyelids, and for a tiny fraction of the price as compared to Singapore (just don't get me started on how @#*^ing greedy many of Singapore's plastic surgeons are!). It just so happens a friend did hers at this clinic last year and I would like to recommend it since the result is very good.
She wasn't happy with her earlier procedure and also wanted thicker lids. Dr Kamol did the correction, as well as harvest fats from under her chin and re-injected them into the outer parts of her upper eye region to lift them up. Now she is a happy camper.
The clinic is located at the basement of Union Mall, which is accessible via Phahon Yothin MRT station. From what I found online, if it's a simple upper blepharoplasty procedure, Dr Kamol charges only 25,000 baht (approx S$1000).
1000 baht is about S$40 to S$43 depending on the exchange rate.