Hello, I come to present you a little accesoire that I use all the time! it is the toutch-mi a French version of the bltoutch that is much more affordable but just as effective !
I use it on a 3 ender since soon 1 years and I am totally satisfied !
the toutch-mi use magnet and a photoelectric principe to measure the bed level, it also have a led indicator on the top and a magnet is disposed in the end of the axis to arm the toutch-mi and let the sensor go down.
you can buy it on this link : https://www.hotends.fr/fr/home/64-capteur-auto-leveling-touch-mi.html
is you want to use it you need to have a marlin version of your firmware and do some small adjustment to make it fully functionnal !
you can see several photos below