I had the same perspective when I started riding as well, as a 54 year old with a bad back, I thought I would like the more upright riding position of a hybrid. It didn't take long to find that this upright position, while comfortable for short rides (up to 10 miles), was not so comfortable on longer rides. As my cycling fitness improved, I switched to a touring bike with drop bars, a more aggressive position and found it to be much more comfortable on longer rides. I did 650 miles last month on my drop bar bike and had absolutely no problems with my back. There was a transition going from the hybrid to the drop bar bike, but it didn't take long before all my riding time was spent on my touring bike. I also suggest you try a cyclocross bike which also has dropbars, but with it's wider tires has less of a harsh ride than that of a skinny tire road bike.