We're on a cruise ship that's docking for one day at Civitavecchia on Monday May 27th, 2019. I believe there will be a total of 5 cruise ships at the dock that day. Since the train to Rome is highly recommended I suspect there'll be quite a scrum for people going to/from Rome. We plan to get off at Trastevere Station in Rome, not Termini. We've been to Rome before, but not the Trastevere neighborhood. This will give us a day of slow wandering on the back streets instead of huge crowds at the more famous attractions.
The ItaliaRail web site will sell me tickets online for the trip, I just don't know if it guarantees seats. Since Trastevere Station is "downstream" from Termini on the way back to the ship, I'm concerned about purchasing a ticket then not being able to get on the train and "missing the boat". We're both older and creaky and it would be difficult for us to stand for the trip, and I don't know if the train allows standing anyway.
I've been researching Trastevere (Thank You Rick!) but I'm open to any recommendations for must see-sights or inexpensive restaurants.