I've cruise solo on Norwegian, and it was a fun time. It was on the Norwegian Epic back when they had the studios for solo travelers (I'm not sure if they still dedicate those to solo travelers...) and a solo traveler lounge. I would meet up with other solo passengers in the evenings for dinner. And during the day, I just did my own thing - worked out, lounged by the pool, explored the ports.
I think I would sail solo on Disney. I'm a big Disney fan - I justified the cost of a
Disney cruise for myself and a guest, so I think I could justify the cost as a solo cruiser, too.