I really like my Elmarit-M (see example below- shot nearly wide-open, with an M3 on Tri-X...). For what it's worth, the Hexanon-M and the Elmarit-M are very similar lenses. The optical formulas are not identical, but the results are similar at most apertures, and the size, weight, handling and ergonomics of these two lenses are nearly identical. They are both excellent lenses; and while not especially heavy (even in RF terms) I'd still love something even smaller and lighter for a minimalist travel kit, if I could get acceptable performance cheaply. I'd sacrifice speed for size here.
If I had the budget for a new lens, I might look hard at the Summarit-M- it intrigues me. I've seen a few prints from this lens, and they looked great- and the reviews have been very good. Being (if only a little bit) smaller, lighter, faster, and cheaper than the Elmarit-M, (both new...) it would be tempting- if I had the budget.
Realistically, in your situation, see what you can find in the way of a lens you can get in your time-frame. Many lenses mentioned here will fill the bill nicely as great performers and excellent travel companions- the Elmar-C and the CV APO Lanthar also especially come to mind as good, small, and affordable 90mm lenses. See what sort of a deal you can get in your buget and on time for your trip. Good luck, and have fun!