Power inductor's staturation current for buck converter
That's right, saturation current should be equal or higher than peak current.
Margin depends on the core material.
When it saturates, the inductance might drop slowly or rapidly.
And at the saturation current, the inductance has already dropped somewhat.
If you want to be super conservative, you could select the inductor so that the rated RMS current equals the peak current.
It does sound OK to use inductor with 1.2A saturation current with 800mA peak current.
Having an inductor with larger current ratings usually have smaller resistance, which improves efficiency.