Re: Rooting...isn't what it was.
Sounds like you need a phone running Xiaomi's MIUI.
You can download and install just about any ROM version.
You can back up everything to the MI Cloud or your PC
You can update via the phone itself, or buy using the MI suite on your PC to contact the MI update server directly - sod waiting for the phone carrier to offer it.
MIUI is installed as standard on a wide range of Chinese sourced phones now, and can also be installed on some branded phones from Sony, LG etc.
Just make sure you get the "Global" version if you dont read Chinese.