timerone.com
Pomodoro is easily configurable with the ability to add additional timers and to set predefined break activities. I like to add a few leg and core exercises (variations of squat and plank) and some stretching. Helps me to remember to move away from the monitor and relax the brain.
One challenge I had was because it was a web app, it acted weirdly compared to if I had done it as a native app.
You say you want to move from the monitor and relax the brain but your timer will not run if I turn off my phone screen and do something else (tested this btw). How do you plan on fixing that? I ask this because when I did it, I managed time client side so super curious what you would do.
It kind of worked too but I'd be a liar if I said it was better (clocks are unreliable AF) than just letting some backend handle that kind of stuff.
I need to click on countdown timer. Fine. Then need to hit the few pixels by few pixels large arrow up to increase from 0 to 1 minute. That makes this essentially unusable in practise. It may work in a controlled environment where there is good light and a steady hand, but if I need this outdoors while walking, no way.
Make those buttons bigger.