Welcome to the forum!
You might look at the 4053TSW, which is double action only, or the 4013TSW, which is double action/single action. Here's my 4013TSW, which should look a lot like your 6904:
I don't know of any books to recommend (someone else will probably chime in here) but here is the magic decoder ring information for the third gens:
FIRST TWO DIGITS
39: 9mm
59: 9mm
69: 9mm double stack compact
10: 10mm
40: 40S&W
45: 45 ACP
35: .357 TSW
THIRD DIGIT
0: standard model
1: compact
2: standard with decocker
3: compact with decocker
4: standard with DAO
5: compact with DAO
6: nonstandard barrel length
7: nonstandard barrel length with decocker
8: nonstandard barrel length with DAO
FOURTH DIGIT
3: aluminum frame with SS slide
4: aluminum frame with carbon steel slide
5: carbon steel frame and slide
6: SS frame and slide
7: SS frame and carbon steel slide