I know you keep answering these - and I read it all, but I have been burned twice on lapel mics already, and I did all my research those times as well. I am not much of a sound tech, but I'm all the church has to solve the issues. Medium-sized sanctuary, sound system that dates from the early 80's (I'll be replacing most of it soon), pastor who ranges from a whisper to a shout, and so far, cheap lapel mics that have delivered very little , just as you indicate. Based on your suggestions, I have been looking at the Sennheiser MKE-2 60 Gold. Am I on the right track?
That should work fine. A Countryman B3 would work, as well. A headset microphone would help keep the audio level more consistent, since it stays the same distance from the source when they turn their head, etc.
It sounds to me like you were having trouble with the wireless bodypack being overloaded by a loud talker/yeller. Read the manual for the wireless system you have and look for a way to pad down the input from the microphone. No matter what you do back at the console, the signal will still distort and sound nasty since that problem comes before the console.
Set your gains conservatively. I have learned to leave about 3dB less than what I think it should be, especially during soundchecks. People almost always perform louder than they practice.
Maybe you should try some of the other steps first before buying a new microphone. Oh, and learn how to use a parametric EQ if you don't already. Put that on the mic, maybe with some compression if you have an open unit, and that should help keep things under control.