Haggling at Benson for Bed experience

Anyone have experience in Benson for bed recently (within 1 yr plz). I am after a mattress and is original price £999. The current offer is £899 and interest free finance. I managed to find online promotional code for maybe extra 10% off and cash back, but still quite expensive. How likely they will reduce the price in store. Also I want to pay with credit card and use finance at the same time, but it seems you are only allow to choose one method of payment.

Does one know Benson's sales pattern, how often they do big sale?

Any advice will be good. Thx

Unfortunately I have back problem. Since I'm planning to change the mattress, I need to make sure it is the right one.