If you're looking for manga similar to Santa Company: Christmas no Himitsu, you might like these titles.
Noel Christonbel is Santa Claus no. 29. He and his reindeer, Rudolf (in human form) visit children on Christmas day and give them presents - whatever they ask for. However, what happens when one of the children they meet doesn't want anything... and instead feels he should die?
Being left alone on Christmas Eve, Ten is mad; her brothers have all cancelled on her. But then a strange boy comes to the rescue and claims that his name is No. 10?! After that strange night, she wakes up to find a name tag of the boy who is named Tohga. With determination to find him in her mind, she sets foot to find him and eventually ends up in the very school that he is from.
This story features the Santa Claus team that takes care of Shirokuma City. Toma is in charge of keeping the reindeer and sleigh going, and he works with a team of cute female 'Santas'. It's up to them to make sure Christmas goes on without a hitch!
Kaji and Yuki have been dating for one month. On their first Christmas Eve together, Kaji thinks there will never be a better chance to lose their virginities, but Yuki is worried…
Wreath, a Junior Santa, fails in his task and has to leave the North Pole. His helper, Mr. Reindeer, has always wanted him. He had been willing to wait but now he's out of time so, before Wreath leaves, he seduces him.