You could always wit until they release a 9.1 beta for the new devices, I'm sure it won't take too long.
Also, you can restore a 9.1 backup to a 9.0 device. Just back up to iTunes. Find the backup and edit the info.plist, search for 9.1 and change it to 9.0. After restarting iTunes you can now restore that backup to a 9.0 device. I did that for my new Mini.
There are no changes to the health app in 9.1 as far as I know so I can't think of a reason why the data wouldn't be compatible and if it isn't you can always reset the new device and wait for the 9.1 beta.