Winging Italy in July

Yes you can as long as you have internet access or a smart phone. Download the booking.com and any hostels apps. Also download the trenitalia and italotren apps to book rail travel. Florence and Cinque Terre are both over run with tourist so book lodging well in advance; the other towns you can wing it.

It is wise to plan ahead.
1) Best to do your research for all areas prior to arriving in Italy.
2) Book your first and second lodgings, recommend Sorrento for the Naples area. Visit Capri, Amalfi Coast, Pompeii and Naples.
3) Hostels don't provide the best privacy, so select carefully. B&Bs are best.
4) Florence, two museums are a must see, Academia and Uffizi. You may need to book them sooner than when you are in Rome.

Thanks for the replies, very insightful:)

In Rome you'll spend a lot of time in line--hours, not minutes--and may very well not get in at all if you don't buy tickets to the Colosseum and Vatican Museums in advance. The Borghese Gallery requires advance purchase. If you don't care about seeing those places, that's fine. The Colosseum is very impressive from the outside, and that's free. Rome is great city for wandering around, and many churches are free.

The Capella Sansevero in Naples sells out in advance. I know the Duomo in Milan sells tickets online for the roof; I don't know whether there's a risk of a sell-out there.

I would be very, very concerned the hostels in relatively convenient locations will be full if you don't reserve a bed. The balance between supply and demand seems more reasonable in Naples, so there's probably less rate risk there.

Tickets for the fast trains (Frecciarossa, etc.) will be considerably higher if purchased at the last minute than if you grab them soon after they go on sale. To see that in action, price out a Roma-Firenze ticket for today or tomorrow and then check the price of the same train/same day of the week for the latest date now on sale (which might be in early June--I haven't checked). Train sellouts are very unusual in Italy, so that couldn't concern me.

https://www.trenitalia.com/en.html << goes everywhere

https://www.italotreno.it/en << won't get you to Cinque Terre

Trenitalia requires that you use the Italian city/station names: Napoli, Roma, Firenze, Milano.

People who were in Europe last summer said the crowds were horrendous. Your planning should assume that this will also be the case this year. It's probably safe to assume that some attractions will be sold out long before the week before your trip.

I also think with hostels, they may not go up to 40-100 euro, but if they are still cheap, they will DEFINITELY be booked beforehand. I forgot to book accommodation for the weekend of the Rome marathon (a high demand time, even though it was March I believe?) and even the hostels were booked SOLID. My friend and I had to share a twin bed in a friend of ours' hotel room.