Anyone have experience with this? In looking around some of the sites, it looks like they generally want around 100% supplement if there’s only 1 person in a room, and don’t even give you the full choice of rooms. Seems ridiculous to me… if it’s going to cost me double, I might as well bring someone along.
Have a look at Holland America. They’re one of the more singles-friendly lines, and generally charge less than other lines for one person in a double-occupancy stateroom. They even have one or two ships that have some single-person cabins.
They also have a “matching” program, but it’s fairly random - they’ll set you up with someone of your gender, but there’s no telling what their age or personality will be. As a temptation, if you happen to be the only person opting for this program on any given cruise, or there are unbooked cabins available, you’ll get a cabin all to yourself, but only pay the regular fare.
If you’re paying, I’ll go! 
My sister went single on Holland America.