Glad you found your bag!
You said you are looking for a sleeping bag for your husband, but he doesn't like mummy bags (constrictive I suppose?) and rectangular bags are too heavy. I have two suggestions of expanding mummy bags for you.
I've mentioned both of these before, but the point here is that these both have variable girth.
1) Synthetic: Snugpack pertex bags
Mentioned above.. Most Snugpak bags have an expanding stretch baffle system. This is basically a flap and extra zipper which runs the length of the bag. You can unzip the bag fully, open the baffle, engage the second zipper, and the bag expands by 8" at the top and 4" at the bottom. This makes for a huge bag, about 68" in circumfrence at the shoulders. I can easily fit myself and my GF in these bags.
You can get these on sale occasionally. I have 5 bags from this company, due to a shipping error; and so have an extra Micro (800g, 5'C, baffle, pertex), and an extra Travelpak Lite (700g, 7'C NO baffle, no pertex). The 'low' temp I quoted there assumes you are wearing an insulation layer.
2) Synthetic or Down: Montbell bags with the "Super Stretch" system.
These have a series of inner and outer circumfrential stretch baffles which allow the entire bag to stretch lightly to conform to the user. The long bags stretch at the shoulders to about 75" Montbell has the world patent on this system, so no one can copy it. There are actually numerous benefits of having stretch baffles, one of which is that the inner baffle pulls the inside shell away from the outer shell, continuously and automatically maximizing the space between the shells, and therefore the loft. I get more than 2" single layer down loft from my #7 alpine (460g, 10'C).
Many reviews online; never seen a bad one.
I own three of these bags and I love them. I toss the #7 in my pack even if I'm staying in a hotel!
For volume comparisons, Western Mountaineering's excellent wide mummy bags$$$ (wish I had one) are cut with up to 66" at the shoulders, but do not have stretch baffles, so you are always heating the extra interior volume.
Knowing your preference for synthetic, Jane; I'd recommendt the Montbell Burrow Bag series, if you want to pay that much, then the Snugpack second.