Poor people in Rome were just a little fraction of poor. At that time Rome itself was what we call a small city today, vast majority of people living outside and poor people inside are mostly slaves of the rich inside, no "ordinary free Citizens". Beside that "apartments" never exists in Rome, there were various size of Domus (houses) with "apartments" for servant, surveillance etc but they were nothing like what we call apartments these days. The most similar thing conceptually can probably be named "colonial homes".

Yes, and Insula are for their servant, small commerce etc, but they are not like today's apartments, they just might look like. Upstairs people live, downstairs people commerce, produce bread, creates leather shoes, vases, ... with animals in internal courts since source food from outside is not that automatic and quick etc.

Years ago I see a reconstruction from a famous historian (Alessandro Barbero) about ordinary Roman's life, unfortunately I can't find it now...

No, insulae were where everyone except the wealthy lived in urban environments including the upper middle classes. And what you're describing is what my city calls "mixed use" and is a corner stone of how apartments work in a lot of modern cities. Small apartments packed in tight above commerical spaces, with the commercial spaces disconnected economically from those living there except from sharing a landlord. The largest difference to today being that the moderately wealthy (ie. upper middle class that still lived in insulae) preferred the lower residential floors, which is a trend that continued until the advent of elevators.