Hi,
I don't have a Fiat 500 (I would love too!
) but a 2 door Yaris.
I did try to put the baby seat at the back when my daughter was born, but found it completely impractical (I had to tilt the baby seat so much to get it out that my daughter was facing the ground!)
In the end, as I could not afford to change car, I did put her on the front seat without the airbag on.
Yes - I was told it is not as safe but it was the only reasonable solution.
The plus points - you don't need to bend and twist yourself to reach the crying baby that has lost its dummy, and my daughter was able to see me so she was therefore much more easy to travel with.
I saw really benefits of having her at the front - but I drove extra carefully during that time.
And soon as she was the minimum size required, she moved in a forward facing seat at the back.
Hope it help