As a back of the fleet sailor my advice would be to go on a training day.
I used to struggle when it was windy but I went on a training day, it was a windy day, and having Gordon Barclay alongside in the coaching boat shouting instructions across I learned a great deal in a very short space of time. Free coaching from people who know how to get a Solo to work for you!
That day I ended up sailing upwind with the centreboard at least half up, the cunningham on harder than I thought the sail would stand and the traveler almost right off. A total revelation, I had never used the controls to that extent but it worked and nothing broke nor has broken since.
I have a 'B' plan sail, which is a cut down old sail. It basically has the bottom section cut off to where the bottom batten is on the luff, therefore just four battens. Any sail maker could do it for you. I don't know how useful it is other than a cruising sail, you certainly lose too much downwind to make up for any perceived gains upwind.