A stress-free day is built, not found
Peace of mind is mostly infrastructure - sleep, movement, light, and a boundary around the working day.
People look for calm as though it were a state to be reached. In practice it is closer to infrastructure: a set of conditions that make calm the default rather than the achievement.
The conditions
Sleep. Nothing else on this list survives without it. A tired brain reads ordinary difficulty as threat, and no amount of technique compensates.
Movement. Physical activity is among the best-evidenced interventions for anxiety and low mood available. A daily walk is not a small thing dressed up as a large one - the effect is real and it is reasonably quick.
Light. Morning daylight sets the body clock, which sets sleep, which sets everything else. Fifteen minutes outdoors early does more than most evening routines.
A boundary. A point in the evening after which work stops. Without one, the working day expands until it occupies all available time and the mind never gets the signal to stand down.
Breath. A minute of slow breathing - out-breath longer than in - interrupts the physical stress response directly. It is the fastest tool on this list and the one most reliably forgotten in the moment.
Where this stops being enough
Ordinary stress responds to ordinary measures. Persistent low mood, anxiety that does not lift, sleep that stays broken for weeks, or losing interest in things that used to matter - these are not failures of routine, and routine will not fix them. That is the point to see a doctor or a mental health professional, and it is worth doing early rather than after another six months of managing.