Loose fill for the win!
“"If you need to add more, go with loose-fill insulation rather than fiberglass batts even if you already have fiberglass. Loose fill is usually composed of cellulose or fiberglass and lets you cover joists and get into crevices. You can rent a blower and do the job yourself for less than half that cost of a pro, but it’s a messy job and you have to watch your step so you don’t go through the drywall “floor” in the attic.”