Getting from Sorrento to Naples in June

I have read that the Metro del Mare ferry is the best/safest way to
get from Sorrento to Naples and that there is a bus that takes you
from the marina to the train station.

It's a matter or preference but IMHO it's a lot more direct (and cheaper) to take the Circumvesuviana commuter train or Campania Express train (seasonal) from Sorrento to Naples. Both arrive at Garibaldi station from where you can just walk inside to adjacent Centrale station to catch your train to Rome. It's the way I'd do it, anyway.

https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule
https://www.sorrentoinsider.com/en/campania-express-train-schedule

(Editing to correct misspelling of Garibaldi)

If you're simply trying to avoid the Circumvesuviana train, then take the 10:19 Campania Express train (arrives 11:09 at Napoli Centrale) and the 12:00 Freccia train to Rome (arrives 1:07). That's simpler than ferry plus bus/taxi transfer.

There is no reason to be afraid of the Circumvesuviana. Really.

Thank you all for your replies. I think the train definitely sounds like the less complicated option.

Circumvesuviana is hot in June, sometimes crowded and quite often with hard working pickpockets. That's why I prefer ferry. On the other hand CV is faster with one short transfer in Naples.

Circumvesuviana is hot in June, sometimes crowded and quite often with
hard working pickpockets.

Pickpockets are not just a caution on the Circumvesuviana. The same care that should be taken with valuables on that train should be taken in other locations and on other forms of transport in Italy as well. But yes, the train can be warm. The Campania Express does have air conditioning, if that's a deciding factor.