Good news about single supplements...
Everybody is always looking for 'no single supplement' opportunities. The good news is that two of Viking's ships, Viking Prestige and Viking Legend, offer single staterooms that are priced accordingly. Both ships will sail the Danube Waltz itinerary in 2015. However, be prepared to book early because the single staterooms are limited and they do sell out quickly. A Viking representative also told Journeywoman that since the beds in any regular stateroom or suite can be configured as a king or two twins - they do see a good many passengers who travel "solo" with friends and configure the beds to be two twins.