If you wear a different orthotic on the right foot you just have to ensure that one doesn't lift you up higher...ultimately giving you a leg length discrepancy. Maybe have your podiatrist have a peak at your old orthotics to make sure that it will be okay for comfort measures.
Speaking less from the "medical" side and more from the "common sense" side....I personally would take both pairs with me to Poland. Your feet (and the rest of your body for that matter) are getting used to their new biomechanics due to the orthotics. If it's so much of an adjustment that your feet are sore and your old orthotics make it feel better....wear the old ones for a little while.
BUT...as I said before, don't mix and match your old right with the new left unless you know one doesn't lift you up more than the other.