You added the "just". Becoming a better person is probably the best thing you can shoot for, though obviously it's not a trivial process and requires significant effort and intention. I mean, what else can you do? You're the one that has to live with yourself.

Even if the whole world is going to shit, if you desire the happiness and wellbeing of others, as a deep internal orientation, this itself is its own form of happiness which is not subject to anything external. Since this thread already has Buddhist vibes, you don't have to take my word for it and can refer to metta (loving-kindness) as its own practice in addition to mindfulness.

The way they've explained it is that immorality is usually based on desire and aversion. And constantly giving in to these things creates a dependence where we're never satisfied with what we have. Having a structured moral code that allows for observing these mental qualities without giving in to them eventually leads to their reduction because we're breaking the habit pattern. Once your desires and aversions are reduced then you become more satisfied with what you have; ie eliminating depression in their case.

Actionable advice: be generous and notice how it feels. Then just be nice for the pleasant satisfaction it gives.