The gent who mentioned parts alteration makes an excellent point. Last year I bought a used K frame that some bubba* had worked on. I had to replace a lengthy list of parts. Some worn, some ruined by bubba and a couple that shouldn't have gotten past the inspectors.

With that out of the way, the number one rule of trigger work on the J frames is not to touch/change the hammer spring. Given the light weight and short throw of the J frame hammer, it needs a stout spring for reliability.

Given that, you might install a new, factory or Wolff, stock spring and give that a try. If you still think you need more weight, look to the trigger return/rebound spring.

The double action revolver has a comparatively long trigger stroke, making a negligent discharge rather unlikely-so long as you practice the "off target, off trigger" safety rule, which you should practice regardless of weight of trigger pull. It also has a century or so history of some slight modification to the trigger weight to enhance your ability to hit what you're shooting at and not some innocent bystander. It does help considerably from the liability standpoint to have that work done by a certified armorer. [The factory used to bless a slight shortening of the trigger return/rebound spring in armorers training. Don't know if they still do, but the Performance Center offers factory trigger work so it would seem to apply.]

* Bubba had some skills. I suspect a "gunsmith" who doesn't understand the workings of a S&W revolver.