About the only difference (for holsters) in any K-frame S&W will be,,,
Some have shrouded ejector rods and some don't,,,
And that really doesn't have that much effect.
The popular polymer-frame M&P autoloaders are obviously not K frames.
S&W has recently sold a few J frame .357Mag revolvers with scandium alloy frames and stainless steel cylinders under the "M&P" moniker. The two that come to mind are the M&P340 (concealed hammer) and M&P360 (spur hammer); there may be others that I've forgotten about.
The M&P340 fits most holsters for the Models 40, 42, 342, 442, 640, and 642. The M&P360 fits most holsters for the Models 36, 37, 60, 437, and 637. FWIW most J frame holsters that don't have a retention strap will fit any given model; however, the retention straps may differ for the spur, shrouded, and concealed hammer models. Also, many of the M&P J's have relatively tall front night sights, which may not fit the sight channel on tightly-fitted holsters made of rigid materials such as Kydex.