I bought my new mattress last december in Marina I actually don't remember the name of the shop but is between zara home and the last starbuck's shop in Jbr walking.
I found a good deal and they sell also tempur mattres which is the best brand in the world but also very expensive!!
Goo Luck
Had terrible troube with Home Centre. Got a brilliant one from the bed shop opposite MOE near the Police station... Cant remember what the shop is called!