Italian train booking sites

Trenitalia will give you the best rates with discounts for advance purchases. Seat reservations are included as they are mandatory.

We never lock our luggage to anything but one of us makes sure to keep an eye on it at intermediate stops.

I don't use 3rd party vendors. Never had any issues with Trainitalia.

Italo is a private company that competes directly with with Trenitalia. You can also check their website to see if they are competitive for the destinations you want.

Both Trenitalia and Italo have excellent phone apps and you can use them for boarding passes. (Unlike Croatia Airlines, I discovered this week, but that's a different discussion.)

Also, if booking a Frecciarossa to Puglia, is it possible to reserve a seat.

All Frecciarosso tickets include a reserved seat.

The two Italian train provider sites are Trenitalia and Italo.

Trainline has the advantage of showing both companies. So you can lookup prices and book trains on one platform.

For Italy Trainline does not charge a booking fee, as both Trenitalia and Italo still give travel agents a commission. And Italo actually uses Trainlines' systems when booking combine regiona/Italo tickes.

So in this case there is a case to be made for using trainline. Another advantage of Trainline is that it copes well with tourists who are not always knowledgeable in the exact spelling of Italian place names...

(Try booking Florence to Zurich on Trenitalia...)

Seat 61, a trustworthy site for info about trains, suggests when using sites such as Trainline are useful and why.
https://www.seat61.com/train-travel-in-italy.htm

The Trenìt! app works well on IPads and phones to see schedules for Trenitalia and Italo.
You can sign up for free on both companies’ web sites to get updates once you book tickets.

No need to lock your luggage on board.
Just sit where you can see it, get up and check it at each stop till the train moves off again.
Keep valuables always…..always…..on your person, and don’t put your daypack in the overhead rack and fall asleep.

We are a little more relaxed than some of the above postings. I will put my backpack on the overhead rack BUT always wrap one of my straps around a rib of the rack. That way if someone would grabs it, they will not get far since it is hooked to the rack. Second do not lock any luggage to any part of the train. Real embarrassing if the train is pulling out and you are still trying to unlock your luggage. We will lock our carry on bags together in the storage bin under the idea if someone grabs one bag the second bag is an anchor and a surprise. I can always carry off both bags and unlock later if necessary. BUT. --- to the best of our knowledge, none of our precautions have ever been tested. I think luggage theft, like pickpockets, are over rated. It can happen but a few precautions go a long way in preventing any problems. In over a years travel in Europe over a forty year period we never had any problems. Means little but there is always the next trip.

Trainline, may be ok for booking. But, we had an issue when our French train was cancelled and Trainline's customer service was nonexistent. I use Trainline much like I use Booking.com, I use it as a search engine but only book with them as a last resort.

We've never locked our luggage and never had an issue, though we keep an eye on it. When I'm alone on a train, I try to keep my luggage right next to me and put my leg/arm thru a strap in case I fall asleep.