The supplied reference describes happiness as a main character property affected by active boosts. Keep an eye on it as part of your routine rather than waiting until a low value becomes a larger management problem.
Official Big Ambitions screenshot — source.
Use activities and goals deliberately
The reference lists personal goals, leisure activities, and books among the ways players can gain happiness. It also distinguishes activities that provide temporary boosts, so plan them around your character's schedule instead of assuming one action is permanent.
Official Big Ambitions screenshot — source.
Avoid stacking the same effect blindly
According to the reference, activities with the same effect name do not stack their happiness value; their durations can still combine. Some exercise activities can also use energy and hunger, so judge the full character-state tradeoff.
Validate values in your version
Durations, percentages, and activity lists can change. Check the in-game character information and test one routine at a time before building it into a long-term schedule.