I have done three solo coach trips since my husband died.
The first step is sitting next to a stranger on the coach. I have been lucky. The first time, I had a seat to myself, but the two ladies behind me invited me to sit with them at dinner, which I really appreciated. On outings I did my own thing, which was fine.
The second time, I was next to a fairly large man, but I had the aisle seat, so was not-too squashed. He wasn’t overly talkative, and we had no other contact throughout the day, so it was fine. At the end, he shook hands and in a slightly quaint way, he thanked me for my company on the journeys.
The third time, the lady I sat next to was a widow too. We got on extremely well, and stayed together for the rest of the week as we both wanted to do the same things.
So try not to worry. It will be fine. Enjoy your trip.