Have you considered trying owens corning 703 instead of wool? Much better absorptive properties.
I originally started looking for 703 but it seems to be fairly hard to find in Canada, while the various Roxul products were broadly available. I did some poking around in absorption vs frequency values and IIRC Safe & Sound was pretty similar to 703 although 2x the thickness.
Roxul also makes a semi-rigid that I am using in a few places (guess I should get around to covering it with cloth eventually) but most of it is still in the wrapping acting as a bass trap in a hallway where a lot of bass seemed to be piling up. Nobody seems to talk about implementing bass traps by dumping a bale of fiberglass or rockwool in the corner (hey it comes wrapped in a free membrane), probably some petty aesthetic thing.
I need to get some treatments up in the HT area so will do another look around to see if I can find 703 this time.