Some insulation options

Spray in foam is becoming more and more popular  in that it seals and will not slough down or under normal situations, compact and loose R factor.

There are kits that you can use if this is something you are considering doing yourself. A shop I used in Sweet Idaho was a 100 year old barn converted into a cabinet shop. The entire building had been spray foamed in which did an amazing job of insulating what would have been a very difficult to do any other way. It did a noticeable job of creating a sound buffer as well.

The only issue we dealt with was mice and other pests getting into the foam. I would suggest preventative pest control if you are considering this option.