I sailed two weeks back to back on the Jade out of Venice, around the Croatian coast and Greek Islands. It was an absolutely amazing trip, both in terms of ports visited and the experience on board.
I was little nervous about 'downsizing' to the Jade as a solo traveller, having only previously been on the Epic, but in fact it was fine. In some ways, the Jade is better than the Epic because of the increased opportunities to view the sea from wherever you are. The trade-off is in entertainment space, so there was less variety on Epic and, I felt, a distinctly less-polished entertainment offer (although some individual theatre acts were excellent, and many of the solo performer at the bars and lounges were excellent - don't miss Fire and Ice or Willian).
My cabin was an inside, and I actually liked the extra space it had compared to the Epic studio, which had been designed specifically for solo travellers. The downside is that the inside doesn't have a coffee machine, but my steward assured me I could request one (although I never got round to it). Given the general opportunities to sit and see the sea/ports, I don't feel a balcony or window would actually have been good value. Very few people seemed to use balconies.
Fairly spacious for a solo traveller and larger than other single cabins I've been in. I imagine it might feel cramped if you opt for two separate beds though.
It's the furthest forward inside cabin on deck 10, so may feel some motion in stormy weather. I hardly ever noticed movement though in the weather we had (fairly calm). It's still close to stairs/lifts so you don't have to trek far.
More importantly, it was very quiet with no disturbances from anywhere else.
I found Dubrovnik to be lacking in any atmosphere at all, and with no distinctive Croatian shops/items on offer. I walked the walls and took the cable car on my own, which was easy enough, but overall I was disappointed with this port - actually being there didn't add anything more than you'd get from looking at photos! In contrast, Split and Trogir were much much better and we visited them later in the week.