I did a sailing Croatia type trip last year (though not with Topdeck) and had a great time. I travelled with a friend so we shared a room, but there was a good mix of people on the boat. Some people travelled with friends, while about half the people on our boat travelled alone. Surprisingly there weren’t any couples on our trip. If you’re travelling by yourself you’ll be paired with another solo traveller, so you’ll have at least one other single keeping you company I had an incredible time and so will you! Croatia is stunning! A lot of the boats join up on the docks (all diff tour companies), so there’s loads of other people around as well that you can hang out with. Most people on these trips are there to mingle with others, so being in a couple won’t really stop this.
Le me know if you have any other questions