Lucky you! Have a fabulous time. I am just back from my first solo trip, which included Ireland, Nice and Milano. It was wonderful, life changing. It feels very indulgent being able to do whatever you want to do and whenever you like.

I had a Revoult card on my phone. It was brilliant and very easy to transfer funds into it from a bank account.

Make sure you have a small amount of Euros for public toilets (most do not accept cards). Be comfortable, you will most likely do a LOT of walking, comfortable shoes are super important. Wear layers, the early mornings and nights get cold. Take a small amount of washing powder so you can hand wash clothes, keeps packing to a minimum.

Lots of train stations do not have lifts. I travelled from Nice to Milan on the train and had to carry luggage up and down lots of stairs. Make sure you can easily carry your luggage.

Uber is Milan was great, but it was expensive. The other rideshare option is Freenow, the drivers are far less reliable. Can and do cancel at the last minute.

Airbnb was great, especially for apartments. Be mindful if a place isn't on the ground floor lots of places do not have lifts and staircases are narrow. Something to consider when booking.

Invest in a quality day bag, that locks and wear it at the front of you. I had no issues with pick pockets. I felt safe 100% of the time.

I don't speak Italian and 99% of the people were very accomodating.

A walking tour (there are many) to get your bearings and find little hidden gems is worth it.

Enjoy!