I really like this handgun, I have big hands and double stack 1911s feel right to me.  However, when I shoot this Pro Custom 40 the base of my R thumb just barely touches the safety and moves it a tiny bit which is enough for the safety to be engaged.  It seems like the safety is too light???  I have a P15-45 Limited that doesn't have this issue.  Any easy fix?
Thanks in advance.

I would replace the safety plunge spring with a new one, seems weak. Or the safety detent is too shallow on the safety lever.

Probably one of those huge safeties, like my para.

Like he said above, there is a spring in the plunger tube that does double duty. Pushes detent pins to bear on the detents of the safety and slide stop.  

Pretty easy fix.  For a single side safety look up some YouTube,
Same for a ambi.

Sometimes a different profile on the detent pin is needed, or a new spring.  I fixed one of my paras that had the opposite issue, the safety was a bear to move to safe position.  I pulled the parts and smoothed the head of the detent pin