We do straight NFP - I once read somewhere that the diaphragm isn't really designed to block the migration of sperm very well (especially on fertile days!) - it's there basically as a place to put spermicide, so the sperm hit the spermicide before getting near he cervix.
So.....that means you have to weigh your views on spermicides, which, I have read, have been linked to birth defects in babies, and can cause major infection/irritation in sensitive women. (I stopped using spermicides after I realized they were the cause of my recurrent yeast infections.)
ETA- I was fitted for a cervical cap after Amber was born, and found out that none of them fitted me! I have a very flat cervix when I'm fertile, so the time when I'd need it most is the time that the thing would be most likely to fall off! I was also told that if your husband is well-endowed, and tends to "hit bottom" during lovemaking, then the cervical cap is a poor choice. It can get popped off too easily.
I'm very fertile, too - basically, we have a baby every time I say "Oh, heck, let's take a chance & see what happens!"
I've been charting my temps & cervical fluids. I'm not ovulating yet (16 mos PP, 2nd PP cycle), but know I could at any time, so I'm trying to keep track!
What books have you read already?