I met a couple in southern Chile this past January who had just come back from an air-cruise combo with
Antarctica XXI. They flew to Antarctica from Punta Arenas, Chile (PUQ; easily reached by non-stops from Santiago and other places) and then boarded a boat in Antarctica. They are experienced travelers and were very enthusiastic about this trip. I know nothing else about Antarctica XXI and have no financial or other interest in them, but pass on the information for what it may be worth.