I'm a single/solo and so far Carnival has been very accommodating to me.
The rates are much better than what other lines have offered. If you book early enough they do offer these quasi-single cabins such as 6226 which I had last week on the Triumph. It has a double bed and sofa.
Never do I ever get this lonely in the crowd feeling. No....there are 2700 friends to keep me occupied. 8)
PAST TRIPS= Enchanted Capri
Carnival: Inspiration, Legend, Valor, Destiny, Holiday, Triumph, Splendor, Fantasy
HAL: Maasdam twice, Statendam, Oosterdam