Is there an option for this to have Battery saver defaulted on or even a toggle app on the main screen to one touch it on?
Correct. And exactly as it should be. If you want it enabled all the time, put your phone in airplane mode, remove all the tiles that flip or update, and maybe hide your phone in a drawer under some socks. That should do it.No option to turn it on permanently. Only until the next time it is plugged into the charger, or when the battery percentage gets really low.