I had to see what a “Mummy” sleeping bag was.
Right now on Amazon you can get the Suisse Sport Adventurer Mummy Ultra-Compactable Sleeping Bag for $39.
Blue and Black/Yellow, Double Layer, Compression Sack
1.5 Lbs. MicroTekk Down Like .7 Denier Fill 680 g.
Drawstring Hood and Draft Tube for Additional Protection Against the Elements
Double-Layer Offset [...]