I have a Helsport Svadlen (or something). Extra long and wide. Comfort rated at 0c and as it’s down it’s less clammy than synthetic bags in summer temps. It’s too warm in the med but then it opens out flat which makes it a lot cooler to be under. Very expensive being Swedish but I got an unbelievable bargain from my friends at Tamarack outdoors who used to be the Helsport importer. I paid less half price.
features to look for imho:
Down. High quality/ high fill power/high down:feather ratio = a compact warm bag. If you want just summer use you can compromise on fill power but stick to 90% down otherwise feathers are a nuisance.
Wide at shoulders, hips and foot box = comfort. For big guys you need 85-90cm at shoulders and only a gentle taper from there. You can then turn over inside the bag rather than with the bag.
full length zip that opens up the foot box too. It’ll go flat like a duvet then. This is what you need when it’s proper warm at night.
you can buy “expanda panels” that zip in a hive extra width. I got one from Cirrus. I don’t think they do them any more. If you go down this route make sure the zips are compatible (one of the tabs will a number on it eg YKK #8).
shoulder baffles, hoods and draw cords upgrade the cold range of the bag but that will have been taken into account by the rating. If you never plan to sleep out on a cool night they are a feature you don’t need.
avoid climbing/mountaineering bags/some expedition bags. Designed for racing whippets they are super light yet warm but mainly tiny. I had one and could barely fit in. Hated it.
make sure you understand the temperature rating. The extreme rating is the one you probably won’t die at if young, fit, wearing thermals, and go to bed fed, warm and dry. Comfort means you will probably have reasonable nights sleep again only if you are young, fit etc. different manufacturers use different measures and ratings so check how they have calculated their rating. There really should be a standard.
American and Scandinavian seem to be the brands that cater for proper sized gentlemen.
a good bag is expensive.