If you can find a daily schedule that works for you, an Amtrak monthly pass is actually less expensive than an MBTA commuter rail pass. Taking Amtrak instead of commuter rail means that there are only 2 stops between Providence and South Station instead of about a dozen, and the train is far more comfortable. You get power outlets, a cafe car, and save about 25 minutes each way.

As far as getting to the station, if you live in walking distance to the R-Line, you can reliably get to the station. It's the closest thing Providence has to a rapid transit line, and it runs every 10 minutes or so and goes directly to the train station.