Now I'm curious what phone you are using Cambsukguy. Most 4 year old phones I know don't get updates anymore. Let alone monthly ones.
Which vendor still supports Android on a four year old phone?
Here's a clue. My nearly five-year-old Moto G (the original one) still gets regular updates via LineageOS. There's a new build out every Wednesday and I tend to install them monthly.
It could do with a better camera, but in all other respects it suits me well (though I still hate on-screen keyboards). Even the non-removable battery hasn't been a problem yet. With careful management it will last me six or seven days, though I could squeeze as many as ten when it was new.