That makes logical sense and I can see the benefit of using tyres you already have....other than the hassle of swapping them over of course.
As far as stability goes.....surely that’s down to axle width as much of more than tyre size? Centre of gravity rather than footprint.
Either way though (and not relating to Clive’s situation) personally if I was buying some new rolls with new tyres I don’t see many issues with super singles to carry the weight on the road, and saving the cash for where it can get most bang for your buck.
New axle is going to be wider than existing yes to improve stability when folding but limited by what’s legal in the road a bit. Tyre width and strength will help a bit as well
Big rolls can be scary when folding as there is a lot of weight being transferred about, not impossible to tiip over !