After much research for our May 17 cruise on Divina we stayed at La Casa Sul Mer. We had a wonderful experience and if I were to ever cruise from Civitavecchia again the first thing I would do would be to book an accommodation there. Check out the Tripadvisor reviews for this B&B. I noticed several were written in May. There were three other couples, as equally pleased as we were, in this five room B&B the night we were there, all of whom were also joining cruises. I'd bet at least one or two of those reviews were from them. BTW, this is the only business I've ever seen on Tripadvisor with a 5.0 rating.
As far as location, it was a less than 10 minute walk from the train station and about five minutes to the pickup location for the free port shuttle.