The good news?
The single-sided standard manual safety/decocker assembly can be replaced with an ambidextrous unit.
The bad news?
It's a more expensive assembly, primarily because of the cost of the ambi lever. The factory retail price for both parts runs about $95 ($60/$35), plus installation and whatever taxes may be appropriate.
Whenever a new manual safety assembly is installed, however, the decocking 'timing' has to be checked. This is because the decocking function involves a couple of tolerances, one of which is the engagement between a surface of the new safety assembly and the top of the existing sear release lever, which may change when a new manual safety body is installed in any given slide. If the tolerance and resulting decocking timing isn't within the recommended spec range then a new sear release lever has to be installed in the frame. This involves filing on the surface of the sear release lever which pushes against the sear nose (the bottom of the sear release lever) until the proper tolerance is achieved and normal decocking occurs.
Armorers used to be taught to check for proper tolerance by slowly functioning the lever(s) and 'eyeballing' the timing of when the hammer fall occurs, sort of midway in the lever's movement, and then checking to see if the lever pops up or down once the initial release point is carefully reached by snapping the hammer a couple of times via the thumb. (Spurless hammer guns could be checked by an armorer's wedge being used to catch the partially exposed hammer serrations on the older hammers, or, one of the regular cup end drift punches - the larger one - could be used as a rough Go/No-Go gauge.)
Nowadays, though, armorers are taught to use a specific set of 3 different numbered metal drill bits as Go/No-Go gauges when held under the left side lever at a specific spot within the slide's machined lever recess as the lever is depressed. (The non-cutting end of the drill bits are used as the 'gauges'.)
I've actually gotten lucky and had a new safety assembly drop into a couple of guns over the years of working on 3rd gen TDA guns, and not have to fit a new sear release lever, but for the most part I've had to fit new sear release levers whenever replacing manual safeties.
It can also depend on which end of the recommended tolerance range the original sear release lever was fitted (filed), too, as well as how much wear & tear it's received over the years. Once a sear release lever wears to the point that the hammer 'hesitates' falling when the lever is fully depressed (or, it no longer falls at all) it's usually an indication that either the lever has worn down too short in the critical dimension adjusted by filing ... or the inside of the gun is really, really dirty and parts are starting to stick.
The factory, a gunsmith familiar with S&W pistols or a factory-trained armorer can replace this part for you, and then check to make sure the decocking function is occurring within the recommended range.
FWIW, manual safety assemblies can be ordered in either stainless (plain finish) or MIM (black finish), depending on the age of the gun and the preferences of the owner. I've ordered both for various guns. Some folks like to match the finish of the new safety assembly to existing slide stop lever's finish/material.
Why not call the factory and inquire about having it done, or seeing if a local gunsmith is familiar with S&W TDA pistols?