Switching either way should really be done only after a thorough system flush, but going 12 to 134 is done all the time without such a flush. Going the other way from 12 back to 134 EEFINITELY should only be done after a thorough system flush.
If you can put in the larger condensor, this should make up for the 134. If everything is holding up okay with 134 and you can get the condensor, I believe that would be a good solution to the problem. A new filter/drier at the same time along with a thorough evacuation would be some good steps to take. Don't forget the oil in the system.