Looking for suggestions on the best (and easiest) way to

Easiest way would by taxi - but expensive!  There are executive transfer services available online.

You can go by train - the following website sells tickets, but has some useful info on trains.

https://italiatren.com/en/train/rome/civitavecchia?gad_source=1&gclid=C…

There are buses that do the trip.

https://www.omio.co.uk/coaches/rome/civitavecchia?gad_source=1&gclid=Cj…