The super shad rap is a pretty good lure for that, and is reasonably priced. I can’t recall exactly what depth it is trolled at, however. May depend on speed and how much line you have out (and what kind of line you’re using too).
guy’s are running Headlocks and Mattlocks on short line behind planer boards. on the shallow settings I believe they have about a 3:1 dive curve but sometimes they are only on 6 ft of line. 18 ft behind the board should be your 6 feet.
Where are you looking to use the shallow running baits? There are lots of baits that run shallow out. Check out Thorne Bros website for crankbaits.
Many spinner baits run less than 6 ft trolled. Even inline bucktails can be trolled shallow and it can be highly effective.
If you can give us some more specific ideas many guy’s can give you some input.
I troll using 7″ Shallow Raiders and 8″ Jakes, usually around the 4ft mark. Takes around 30-40 ft of line out to achieve 4ft depending on line diameter and speed of course. I do a lot of trolling around 4 MPH and the 7″ starts to kick out erratically around there which is good for triggering strikes. The Jake has a wider wobble and takes a little more speed to really start blowing out but both are excellent trolling baits.