I am curious to know if you found someone. The South American cruises appeal to me as well, and there are amazing discounts being offered, but my husband is not free to take a vacation of that length.
If I were not already booked for a March cruise I would love to go with you.
Years ago they let you share a cabin with strangers and it worked fine for me. If there were great differences in age or interests it really didn't matter, you just went your own way. On the other hand, I still keep in touch with old room-mates from years ago.