You might consider an M4p which has frame lines that can be used for almost any lens (with some mental adjustments). Peter's advice is good, a serviced M is a good idea and the finder condition (brightness) is important. I have had over time an M6, M4p, M3 and an M2. The one I held onto was the M2 it was simple the most quite M I have ever handled and I like its simplicity.

Good Luck!