We need to get a new iPhone (likely 17e) but the device will run a critical medical infusion device that is very specific in which iOS versions it supports.   

To date we've just been waiting and hoping the manufacturer will catch up and we make the purchase, but at the moment Apple are putting out updates faster than the manufacturer is so it's always behind.  eg. Apple will release iOS 24.3, the manufacturer will work on it and release a version compatible with 24.3, but before they did so Apple released version 24.4 or perhaps 25.1

Question: is it possible to get a selected version of iOS onto a new iPhone (and the new phone also needs to 'copy' over all the data from the existing phone as well).

An other option we thought about was to buy one now, copy the existing phone over, adjust the settings on the new phone to NOT automatically upgrade the iOS, and then just leave it in the box until the manufacturer catches up.   The downside of this could be losing any information from the original phone that have happened since the copy to the new iPhone was made (I guess we can synch photos etc, but there's a bunch more stuff that might be missed).  If we took this option is there any way to "copy" the existing phone contents back over again to grab all the info that has happened since?   Or does the copy existing phone option run the risk of the new iPhone deciding to grab the latest iOS as part of this process.

Or are there any other suggestions?

And before anyone proposes it.  There have been a decent amount of annecdotal reports of people crossing their fingers and jumping up to iOS versions above what the manufacturer of the medical device say they support and running into all kinds of issues, so sucking-and-seeing is NOT an option.  Some people have had it work fine, but it's not a risk we're taking.