Fiona, I know exactly how you feel. I felt the same way before I walked the first time with a friend in May2011 from Leon to Santiago. We didn't quite believe what we were hearing about ease of finding beds, food, safety, and physical demands so we created a rigid walking plan that included far toooo many rest days. We tossed that on Day2 and had a wonderful time!
When I returned home I realized I had caught the "Camino bug." I was infected and the only cure was to return in October to walk the parts we had avoided. I'm still infected, and I have no plans to stop walking, until I can't. You, too, will easily overcome your urge to be ultra-organized and you will enjoy the 'go with the flow' aspect of the Camino--that's part of its magic. It all works out.
I do recommend booking ahead in St. Jean and Orrison to ease your mind about finding a space in those early, most challenging days. Roncescalles, the next destination is quite large and there will be bed for you there. After that continue with your original plan to not book ahead--it is indeed an attraction of the Camino. I enjoyed the municipal and parrochial albergues for their simplicity, low cost, and the sense of community, and I think you, too, will relax after the first few days as you ease into the rhythm of the Camino and feel more confident about the availability of accommodations, and as you develop your own routines. It won't take long to catch on to the way things work.
In short, submit to your "internal battle to be organised" for the first few days, then switch to your plan to "just go with the flow." You don't know what you will like (or need) ahead of time. Have fun!