DP and I have sailed with Azamara a few times. They always have a get-together for solo travellers early on, and also have a hosted solos dinner every evening, though you can dine alone if you wish. Open dining, so you’re not tied to one time or table, which we very much prefer.
Their single supplement is usually 100%, but there are always offers for cruises with it reduced to 50% or even 25%.
When you’re comparing prices, do look at what’s included; all-inclusive cruise lines look most expensive at first glance, but taking into account drinks, gratuities, etc, together with the generally higher standard, they can be better value overall.
I’d always go for a balcony if possible, but I prefer to have the feeling of space that it gives. For some, it’s not a factor.
If you’re not sure you’ll enjoy the on-board experience, look for a cruise that has a stop most days, and ideally docked, so you can walk off and on as you wish. Also, if you pick a European cruise, your mobile phone allowances should work as they do in the UK, so it’s easier to stay in touch. On board WiFi tends to be expensive and slow.