Did you think this project was dead? Well it took a hiatus because I tried multiple variations of my power supply using the Wurth 74488540250 transformer, but I couldn't get it to work without overheating. In the end, someone suggested the transformer was saturating and that I look at a range of transformers by Coilcraft. In particular the LPR6235-123. Now that is a 1:50 transformer with an Isat of 0.9A. This was too close to the one I was using which had an Isat of 0.7, plus I was pretty sure that the high secondary ratio of the Wurth of 1:20 was also causing problems with ringing. However Coilcraft also had a 1:10 transformer with an Isat of 1.3A in the same family, and the footprint was compatible with the Wurth. I got a couple of samples and it works! It is the LPR6235-253LMRB. So this project is back on track. Now I need to figure out an enclosure.