TS, you will not be able to get this price now, Serta had increased the price since 1st May. That time when I heard the news from this forum, I rush down on the very last day to book although I only need it next year.
Anyway, you can try Sleep Center in Kaki Bukit, Eunos Technolink, they are able to give u good discount off the retail price. Another good place is Inges in Little Road (near Paya Lebar)
These shop selling Serta, Sealy and Simmons too, you can ask them to recommend. Do ask where the bed are made from.. as those made in US and Korea and Indonesia used their own material, the feel and price also diff. Anyway all Serta bed in singapore are made in Indonesia