I had no real issue with my 642 trigger weight, since this is a SD weapon not a bull's eye weapon. It is quite stout at 18-19#, but sending 25 or 30 rounds down range was not that big of a deal with me; however my wife had a tough time even with 2 fingers pulling the trigger more than a couple of times.
According to Wolff, the factory rebound spring is 18-lb, and the hammer spring is 8.5-lb.
I ordered directly from Wolff Spring, a PA company!
16670 S&W RP REBOUND SPRING 11-15 ASSMT PAK Pak of 5
23808 S&W RP HAMMER SPRING 8LB PAK of 1
The Rebound Springs "Reduced Power" baggie has 11-lb, 12-lb, 13-lb, 14-lb, and 15-lb.
I chose the 12-lb rebound spring, installed it and the 8-lb hammer spring both just two days ago. I don't have a meter, but I would estimate the trigger pull is reduced about 1/3, so that makes it 12-13-lb. Wife dry-fired several times and she said it was much better.
It is still a stout pull, still much heavier than my 13-1, which I believe is OEM (just worn smooth). I feel safe carrying it like the pocket firearm it is, but it is in the safe until I can get to the range to test it with several brands of bullets. Seems folks are split as to whether this is a good idea. I did it because my wife needed it. I won't use it until it is tested.
Pretty good how-to video here
Part 1
and here
Part 2
Another S&W forum posting with pro / con comments about spring replacement.