I removed my M&P 45 safety.
http://www.burwellgunsmithing.com/M&P2.htm
I bought a multi pack of springs from Home Depot for $4.79 and there is 5 of each in there, one spring in the pack is the perfect size and just needs to be cut to perfect length. Only purpose for the spring after safety is removed is to keep take down lever snug against sear block and under sear.
Not to be an alarmist, but be careful with anything from Home Depot, as they sell some of the cheapest, crappiest junk around. If a product is from a known-good brand, then fine, otherwise it's probably substandard (like their screws and other stuff).