It helps so much to turn your phone off every night and to not leave it charging as you sleep. I have a spare phone that I keep on all day for alarms and whatnot. Turning your phone off every night will help preserve battery longevity and all around performance of the phone.
Sounds like you have a plan that works for you. I admire your dedication to switching between phones every night. The hassle of switching SIM cards and the possibility of damaging a phone in the process make it something that I wouldn't do.
As an alternate viewpoint, I have done the complete opposite for years with multiple phones. I've never experienced any noticeable battery degradation and certainly not early battery failure.