I think you'll probably have to experiment for yourself as even though you may have 'hard' water in common with someone else, the type of hard water you have could be vastly different (different minerals in different concentrations) and that can make a huge difference in what works and what doesn't. Tons of other factors too, like individual detergent, individual wash routine, individual diet and perhaps even individual chemistry... What one person with hard water swears by, another will swear at!
I've heard that vinegar, Oxy-Clean (oxygen bleach) and water softeners like Calgon are all possibly useful additives. I remember one person on the board had huge build-up problems and Calgon totally solved it all! And theoretically the acidity in vinegar should be good to help dislodge/dissolve minerals built-up in fabric...
The very basics though is to avoid using too much detergent and avoid all fabric softener as that's the biggest cause of build-up and stink. After that, just see what works for you and don't worry too much about it...
Good luck with your new baby!