I have spent a few days looking for a soft latching power on/off switch. I have breadboard-tested several designs, including at least these three:
I tested all 3 of them with and without load. As load I used a lux meter project (Arduino Pro Mini, BH1750 lux sensor and Oled display). The 555 alternative (design #1) is on the breadboard at the right. Power cables are at far right:
All of them work (with/without load), but ... all of them start frequently in ON position when connected to the power supply (with/without load, tested physically inserting/extracting the positive power cable from the breadboard).
Just think what may happen when main power returns after a blackout.
Do you have a switch design that guarantees starting at OFF when power is apply, just like a mechanical on/off switch? Bonus: One that does not oscillate when you keep the button pressed?
(I really like two separate buttons, if possible).