I'll echo DWalt's post in saying that your M&P will handle any factory-loaded .38 Special ammo safely, but will be at its best with a 158-160 gr. lead (RN or SWC) service-type load (approx. 800-850 fps). The 148 gr. Midrange Wadcutters will be good at the range, easy on both gun and shooter, and even the Buffalo Bore +P load, which approximates the old .38-44 HV load, will be safe, but will indeed accelerate wear on the gun. If you should encounter any of the Winchester or Federal 130 gr. FMJ for cheap, buy them. It's an utterly wimpy load, being the commercial equivalent of the military M41 Ball, but the fired brass will be first-rate for reloading.
Larry