Hope to relay some of the experience I have had with friends who had gone down this path....
Most of the "universal fit" lasers on the market these days that will attach to the trigger guard are inferior Chinese made lasers that will quickly loosen or fail on a real gun. In addition to having glass fragile electronics, a weak set screw mounting system, they will often prevent you from using most holsters, and their activation method will be inconvenient at best.
Your best bet would be the Crimson Trace brand laser grips. They are a known quantity, have an excellent reputation, and will allow you to continue to use most holsters. I'm looking at their website right now, and don't see any options for the 45XX pistols, just the 59xx pistols. So I don't think you will have any options, unless Crimson Trace had made, and discontinued, an option for the 45xx in the past. Given that the world has mostly moved away from the third gen smiths, this may be the case. If crimson trace ever made laser grips for the 45xx in the past, you may be able to get a New Old Stock pair or used set off of eBay or gunbroker. I have no idea if they did make 45xx grips in the past, but someone else can chime if if they did.