Gurm
Sounds like a good plan. I'd recommend trying eBay or other similar used iPhone sites (This is how I got a 8+ and iPad 7th Gen on 14.x a few months back). Just make sure to message the seller and confirm the version, and you should be all set. Also, Apple's refurbished devices seem to generally be on lower versions, you may have some luck there as well.
Clokwork
Sorry to hear that, I had a similar experience with my old 8+ and iPad after updating to iOS 15 as well. If you're looking for something on 14.x, the stuff in the above paragraph may be helpful to you as well 😃