By Jonathan Allen

NEW YORK (Reuters) - Nearly two-thirds of married couples and people with a significant other say their partner is the most important source of happiness in their lives, according to a new global poll released on Valentine's Day.

And nearly half of all singles yearn above all else to find a sweetheart, with about 45 percent saying finding a partner would bring them the greatest happiness.

"What strikes us when we look at the data is that you have this majority of global citizens who are really looking at home for happiness," said Keren Gottfried, research manager at Ipsos Global Public Affairs, which conducted the survey in 24 countries.

South Africa reported the highest levels of domestic bliss, with 82 percent of settled South Africans saying nothing could make them happier than their partner.

Japanese and South Korean couples were at the other end of the scale. Nearly half said they would hesitate to say their partner was the single best thing in their lives, although they conceded that he or she was the source of at least some of their happiness.

For many couples, about 38 percent globally, the best thing about their relationship was the sex, according to the poll. This was especially true for Brazilians. Nearly 60 percent said that nothing could make them happier than having a good sex life.

But the Japanese, South Koreans and Britons tended to value other qualities in their partner. Only 15 percent of Japanese ranked their sex lives above all else as a source of contentment.

Single people in the same three countries also reported a resilient independence, with only a third or less of single Japanese, South Koreans and the Britons saying finding someone to settle down with was the most important step in their search for happiness.

Single Indonesians were the most preoccupied with finding a mate. Nearly 70 percent said nothing could make them happier, followed by 57 percent of Turks and 56 percent of Mexicans.

But even among couples who lived together, the poll found signs of restlessness with slightly more than a quarter of people in such relationships saying that finding someone else to be with would make them happiest of all.

Ipsos interviewed 21,248 in an online survey in Argentina, Australia, Belgium, Brazil, Canada, China, France, Germany, Great Britain, Hungary, India, Indonesia, Italy, Japan, Mexico, Poland, Russia, Saudi Arabia, South Africa, South Korea, Spain, Sweden, Turkey and the United States.

Fifty-nine percent of the people surveyed said they were married or living with their partner, while 41 percent said they were not.

(Reporting by Jonathan Allen, editing by Patricia Reaney)