Start with the week you actually have
It is easy to plan for an imaginary week: no late meetings, a well-stocked fridge and plenty of time to exercise. A more useful starting point is your calendar as it stands. Look at work, caring responsibilities, travel and the things you want to enjoy.
Choose a small number of opportunities that already exist. That might be a food shop on the way home, a lunch break you can protect or a training session beside another regular commitment.
Give your plan a busy-day version
A routine is easier to return to when it has some flexibility. Decide what you will do when time is limited: an easy meal assembled from what is on hand, a shorter planned session or a walk between tasks.
The busy-day version should be simple enough to remember. It keeps the next decision small instead of turning a changed plan into a reason to abandon the week.
Review the fit, not your character
If a habit keeps falling away, get curious about its place in your day. Was the timing awkward? Did it need more preparation than you expected? Did you actually enjoy it? Adjust the setup before deciding that you need more willpower.
A useful weekly review can be three questions: what felt easy, what got in the way and what would make next week simpler? Keep the answer practical.