You could make your own extra wide winter stirrups. Used to see them a lot when I was a kid before all the light weight insulating materials came out. The best ones had duct tape trapaderos to block the wind and keep you from getting big clunky boots too far home. I do remember seeing the big ugly things covered in duck tape. Even in 1972 duck tape was a miracle material.
I have an extra wide pair of rawhide stirrups on one of my aussie saddles that I can get a pair of winter boots into. Was a saddle my husband used to use a lot but he has only size 9eee feet.
There are some oversized western stirrups on ebay
that are 6.5 inches across at the bottom.