There are not that many options, Homes r Us in Hyatt plaza, then again ID design at The Mall has sale with lots of interesting items now. If you look at something very budget, you can have a look at furniture shops around and in Najma souk.

Also don't discard places like Tivoli Furniture (in front of Al Asmakh mall), and the stores on Salwa Road, next to Decoration Roundabout. You'll be surprised what one can find there.