western mountaineering highlite bag for “wider” people?

I have the Ultralite, which according to Western Mountaineering's website has the same dimensions as the Highlite.

Not sure what your actually body measurements are. I'm 33"/39" waist/chest and think someone only a couple more inches wider than me would be ok inside the Ultralite, and even then, they might not be comfy.

Try the Megalite if you want a looser fitting WM bag.
Also, maybe find somewhere to try them out first.

I think its called the caribou

You're like me – you'll be happier with the 62 inch and larger shoulder girth WM bags. I'm a rolly-polly side sleeper and the 59 inch girth is too tight on my arms when I'm lying on my back or stomach.

Take a close look at the WM Sycamore and Alder. They are identical except the Sycamore has a hood and the Alder does not. Both have the 62 inch shoulder girth; both are rated to 25°F. I've had my Sycamore below that several times on the CT and PCT so I know it's accurate; maybe even a bit conservatively rated.

The bigger advantage is that these are semi-rectangular bags. They also unzip FULLY to make a large QUILT. There are two zippers; one down the side of youre choice and a 2nd across the foot. Ventilation options are unlimited.

My wife and IU have a pair of Sycamores and zip them together; pure luxury.

I have a Mitylite. No hood, semi rectangular. Works as bag and quilt. Had mine overfilled. WM charged me $25 to add 4oz(they billed for 2oz)of overfill. Had this bag down to near freezing and was warm.
I have size 15 feet and find the footboxes on most sleeping bags to be too small unless I go with a semi-rectangular bag.