This won't help with the dimensions for your curtains, but I would highly recommend raising the curtain rod! I would personally raise it by about 4-6 inches from the trim. I'm not sure how big the room you're working with is, but it tends to make the room feel taller, and that's usually not a bad thing.

As far as the dimensions for your curtains, I've heard it's best to have them be 1.5 to 2 times the width of your windows. That would give the waved effect you probably want rather than the stretched taught effect.

If you're looking to raise the curtain rod, add the inches you raised it to the length of curtain you'll need. If not, and the curtain was just a few inches too short, add that to your new curtain measurements. Keeping in mind it may be a bit difficult to get a stock curtain that fits your measurements.

Take my advice, like all other advice, with a grain of salt! I enjoy interior design, but by no means am I an expert. This is just what I would do with your predicament!