yeah, the steel pole thing is an easy enough fix. If you have settling like that in just 3 years, you'll probably want to put them in pretty soon and start keepin an eye for any other signs. It helps to run a level string line from wall to wall in the basement and measure to the joist in question. Then you just find the lowest point, insert support there, and lift until the joist is level.
I'd start with 1, maybe 2 depending on the severity. IF you continue to have problems add more, equally spaced. Remember, if you go from 1 to more supports, don't remove the first until the load is supported by the others. The sudden drop can wreak havok on your doors closing upstairs.