Bro, it is the norma that mattress are marked up about 50% their selling price then they mentioned they have 50% discount. You will see this when you visit Robinsons, Courts, Harvey Norman and other places or brands that sell mattresses.
Mattress is a very personal thing and you have to lie down as long as you pefer to have a better feel what you want.
You also need to balance your budget and the features of the series/model you intend to purchase.