Snugpak Softie Hawk and Snugpak Softie Kilo work just fine zipped in their respective pairs for us.
Excellent! Are you using one of each or a pair of each? And (without being too personal ) are you little people or big people?
Pairs of each. The Kilo's are lighter and better for warm summery weather, the Hawks are heavier and great when you get those chilly evenings.
I'm a 3XL YACF shirt size though Mlle PB would be a S. We do not spend all night in a close embrace.
I have never seen a 'fat' mummy bag, nor an 'extension' for said bag. Sounds interesting in a curiosity sort of way.
We don't have a problem with the zip at all, just with the mats moving.