Nikki, you can try Yin Yin alteration specialist. She's on the 2nd floor of tanjong pagar plaza. I've tried many other alteration places, so far she's the best I've come across.
You can try Micky at Sengkang area. She runs an online bridal store with gowns from US so she knows how to deal with those types of complex boned gowns.
Her number is 64006553