Which power adapter would I need to charge my iPhone in Italy?

For Italy, you need what is known as a Type L adapter. They look like this, and are quite different from what is used in most other central European countries.

Amazon has them, or you can pay twice as much at the airport travel shops. You will probably need at least 3-4 adapters to handle iPhones, laptops, iPads, razors, etc.

You do NOT need any kind of voltage converter for Apple devices since they will operate on 100-240 Volts and 50/60 Hz

Modern chargers adapt automatically to most international voltages in the 100-240V range. If you wish to confirm this for your charger, most have voltage ranges embossed in tiny letters on the back. You may need a plug adapter to actually fit your plug to whatever they use in the country you are visiting. Sometimes those are more easily found in your home country in a store selling travel supplies.

Something else I find handy is an extension cord since I often have to charge multiple items overnight. I have also found that sometimes the nearest outlet is across the room from where I want to use a device. If you get one in the your country of residence you only need a single plug adapter because you have multiple outlets on the strip. Just make sure you get one suited to the power supply of the country you are visiting since many other countries use 220V.

Your only concern may be if you are traveling to a location with an "unclean" electrical supply and if voltage spikes are an issue. If that is the case you can investigate purchasing a surge protector to protect your device.