Room ratios

One thing to watch out for as Ouput555 has discovered (the hard way), doubling sheet rock makes for a rigid wall. It helps with sound isolation, obviously, but the more rigid the wall the greater the peaks and nulls in the low frequency. If you do change the dimensions of the room, my advice would be to fur out and use single layer sheetrock with standard bat insulation behind. The 1/2 inches sheet rock is semi-transparent to low frequencies and acts as a capacitor to some degree--thereby reducing the bass problems.

doubling sheet rock makes for a rigid wall

Good point. A leaky room is far better in bass response than concrete walls. Concrete basements rarely sound as good as wood frame walls and wood floors. The only people who suffer from a leaky room are the others in the house and potentially the neighbours!

I agree with Plato, if you can change the dimensions of your room easily, then do that first. Get that right and then you may not need as many bass traps etc.

If you have total freedom for placement of the right and left speakers, that will help you a lot as well.

My room is 13W x 8H x 21.5 L