You tube has a lot of videos that will help. Also I too have heard good things about the spring from Wolfs. I've read accounts of people using pen springs. Never had the scones to try it myself.
I have owned Sigmas in the past and considered lightening the trigger too, but for SD use, I decided the heavy pull was fine. It did take more practice to get used to it but that is a good thing to do. If I were using it more for plinking or competition, I'd modify it. There is a lot of details on do-it-yourself trgger mods on the S&W owner's forum (can't remember the site's name...) and I'm sure you will find lots of info via Youtube. If Apex has kits for a Sigma, I'd go that route since they have a good rep for quality.
Here's a link to another site that may help. I have an Sigma and learned to shoot it, the thing took some getting used to, but it goes bang everytime and thats what I bought it for.