Month ago I built my own android app that automatically switches on airplane mode whenever the display switches off (and vice versa). Made in 10 minutes with Tasker, it's even in the play store.
Since then I really enjoy life again without any notifications, it's just wonderful.
I just use the moderate power saving mode which disables network traffic of the background apps. Now my 2017 Samsung A3's battery lasts about 3.5 - 4.5 days / charge. If I need to be "urgently" contacted people can still call or SMS me but I don't want any realtime notifications from apps.
Since then I really enjoy life again without any notifications, it's just wonderful.