A water belt is a necessity for any of our deeper/faster rivers and streams. I tried to "jump~float" from one underwater boulder to another on one of the creeks (maybe Shunda or Dutch) in the Upper Oldman system once. The flow pushed me past my intended landing zone and I went for a dunking up to my face-level. Definitely over the top of the waders. I had a belt on and very little water made it in. They were the old-style Cabela's nylon+pvc kind. I would have been in some serious trouble without a belt as I was fishing alone.
I cringe when I see people wading without one on the Bow. It's a great river for getting blown off your feet.
Note: I'm not sure about a wider belt. The logic behind them in other applications is to support proper form and stabilize internal structure. I don't think you would get that benefit from a fishpond or Simms, as they are not designed for it nor are they stiff enough.
I'm eating older too and have to consider issues like this while wading. I don't have back pain but I do have some balance issues from a neck injury (and spinal fusion operation). I think picking wader boots can be very important when you have issues like us.
Maybe investigate an orthotic or new boots that give you the best posture and support you can get. A physiotherapist or a chiropractor could probably tell you what to look for. For me, I made sure to avoid the new lug sole ones as they are just too slippery. I got some with felt + cleats (studs) for maximum traction after my old Orvis ones blew up mid-stream.
https://imgur.com/gallery/fcjMw90