How warm a duvet is depends on the amount and type of fill, not the label. Pick the warmth for your room and a build you can wash, and ignore 'hypoallergenic'.
A duvet (comforter) is an insulating fill inside a fabric shell. Down gives the most warmth for its weight and lasts longest. Fill power measures loft (higher means more warmth per gram), while the fill weight decides how warm the duvet actually is. Down-alternative fibre is cheaper, easier to wash and suits people avoiding animal products. Wool is less lofty but handles moisture well.
Construction matters: baffle-box stitching stops down from shifting, while sewn-through channels are lighter and cooler. In the UK and Europe a tog rating gives a standard warmth number; many US products just say 'lightweight' or 'all-season'.
No trials link duvet type to health. A small lab study found no sleep difference between wool and polyester bedding, while a cooler room (17°C rather than 22°C) improved sleep, so the right warmth for your room matters more than the fibre. Dust mites live in every fill; a hot wash kills them.
17 healthy young adults slept in the lab under different fabric and temperature conditions. Wool sleepwear shortened time to fall asleep versus cotton, there was no effect of wool versus polyester bedding, and people slept better at 17°C than at 22°C.
Washing at 55°C or hotter killed all dust mites. A cold wash removed over 90% of mite allergen but left most live mites in the bedding; detergents did not improve killing at lower temperatures.