<p>I would second the use of a TLR. <br>
The Mamiya C330 is heavy and bulky, with the C220 weighing less but about the same size, but still able to take interchangeable lenses. Two caveats - the film transport on the C330 can work, but in a way that causes the film to buckle, reducing sharpness; and, some of them were heavily used. Even the C220 might be too heavy for you. If the size and weight don't bother you , they are good cameras overall.<br>
I would suggest either a Rolleiflex, (most expensive option) or even a known-working YashicaMat, Autocord, or Ricoh. The completely manual Ricohflex with the geared lenses is very light and compact, has no double-exposure prevention, and you have to use the "red window" technique to advance the film; but the lens itself is excellent (Tessar design) and will give you the same big 6x6 negative.<br>
If you can, try to handle a few of these cameras beforehand. If you are talking to people (vs being completely invisible and unknown while you take a picture with no one else noticing you), what camera you have in your hand is not likely to matter too much ; and the use of the waist-level finder, with you looking away from the person, seems less "direct".<br>
One other option - get a sturdy monopod for your RZ67, make sure it is firmly attached, and heave it over your shoulder to carry it like an old-time photographer (or hobo).</p>