You can just buy any suitably sized canvas messenger bag you like, then use your padded insert. Or get another slimmer padded insert.
For recommendation, look at Think Tank Retrospective, they're really nice.
Another option would be padded wraps which I use; they're very versatile, great with mirrorless and small cameras alike. I just wrap what I need then put them into my everyday regular messenger bag. Its called Domke Wrap, similar to a lens pouch but the wrap more versatile. I also use lens pouches by Porta Brace for any lens and other stuff here and there, but if a mirrorless is all I'm carry, the wrap is all I need for enough protection in any of my bags