Hi fabrizia, and welcome to garden web.

How sunny is the porch? That will determine what will grow happily there. Also, do the windows open, or will it really be like an oven in the summer? If I had a screened in porch, with glass windows for winter, I'd definitely be growing olives.

If you can get your hands on a thermometer that will tell you just how cold it gets over these last few nights (I hope!) of winter, you'll be able to convert that to a growing zone number, and that, along with the sun level, will let you start narrowing down the list of possible plants.

The nightly low temperature is usually around 4 in the morning, I think. A digital thermometer that records the low is not hard to find, and would be more help than a plain one.

Thank you Diggingthedirt,

Olives? What a wonderful idea.
Yes, the porch has windows that can be opended during the summer, helping with the air circulation.

As you kindly suggested I will get a thermometer to record the lowest temperature.
Thank you again and have a great day.
fabrizia