If you're intent on trying out FSU gear, I would suggest a Zorki-6 as perhaps the most ergonomic variant, and the Fed-3 as the most indestructible.
Fedka in NYC sells the J-3. Might be more $$ than the Ukrainian sources on ebay, but your chances of getting a winner are much, much, much greater.
Oh, just looked and I see you're in UK. Fedka is not as attractive an option now, expense-wise.