As long as you aren't banging into the panels, go for mineral wool, same effect, less cost. Something like 2.5 lbs/cubic foot is good. Just remember to cover it in fabric, otherwise, touch it at your own peril. But in addition to absorption, don't forget diffusion, that will go a long way to providing good room response (most all room acoustics is based on the assumption of a diffuse field). Use the panels to create as much of an RFZ as possible and diffusion for the later sounds. If you still have bass problems, you will know it isn't the room. If your monitors are near a wall or corner, then don't use the bass boost as you are already probably enhancing your bass response by putting the monitors near a boundary.