bumping into Meredith in Rome

That'd make a fascinating back story, but I don't think Tom plans that far ahead or thinks that deeply about consequences

He's repeatedly shown to be a improvisation artist, acting on a whim and covering his tracks

He got lucky with Meredith in Rome and exploited the opportunity to the fullest, that's pretty much all

Intentionally seeking out Meredith would only have benefited Tom if he could arrange a subsequent meeting between Meredith and Marge. However, he didn't know that Marge was in Rome, so setting up that meeting would have been a lot more complicated.

Suppose he did manage to pull that off. Eventually, either someone would report Dickie missing or the boat would be found and linked to Dickie. The police would question Marge, and she would give them Meredith's name. Although Meredith would be an eyewitness to Dickie being alive after San Remo, there was a huge risk that the police might show her a photo of Dickie. Then she would become a witness to Tom impersonating Dickie after he was last seen alive in San Remo. Hotel staff might mistake a photo of Dickie for Tom as Dickie, but anyone who knew either of them well wouldn't, so the safer option would be to avoid Meredith.

That risk was also present the way events transpired in the movie. But, Tom had to come up with a plan quickly and maybe didn't have time to think things all the way through.