Welcome to Cruise Mates, there are a couple of options you might want to check out other than a specific "singles" cruise. These forums contain a section called "Seeking Cruise Companions" that seems quite active. This might allow you to find someone to share expenses on a regular cruise. Also, you might want to check out Norwegian Epic. It single cabins which would be full, well singles.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014, 2016, Royal 2017
Star Clippers: Royal Clipper 2015