Unless you have really regular cycles, NFP may not work very well. It's hard to tell when you ovulate, even with trying to track your body temp, etc. Have you ever thought about getting an IUD? They have non hormonal ones, like the copper IUD. just a thought.
not sure about how long you should wait or what brands are good, I just thought I'd give you a little heads up.
I got pregnant while using the Natural Family Planning method. Every cycle I ovulated on day 25 and had an 11 day luteal phase. Well, my husband and I started working out right after Christmas this past year because we'd both gained "college weight" lol. Well, something I didn't realize is that exercise can affect your cycle...I ended up ovulating on cycle day 17 and VOILA! I got pregnant.
So...just be extra cautious, especially if you are planning to start exercising to loose baby weight. Otherwise NFP is an excellent form of birth control and it's what I plan on using again (baby's a month old now).
Oh, and for sure you will want to wait until you are getting at least 4 consecutive hours of sleep a night before bbt charting in order for it to be accurate.
You really can't use BBT's while breastfeeding, unless you have already resumed having regular ovulatory periods.
Using opk's is also not necessary. If you use NFP and want to be safe, you will have to completely avoid intercourse for quite a while before there is any chance of ovulating, since sperm can live up to 5 days in the female genital tract. An OPK could be negative one day, and you might have sex...and then the next day it could indicate ovulation. Then you could be in trouble.
If you really don't mind having another baby, NFP could be a good method. It requires a lot of dedicated effort and charting. And even then...the human body is sometimes unpredictable, and a sudden early ovulation like the one FreshLove describes can lead to conception. If this would not be undesired, it doesn't matter so much. If it would be a disaster, do not use NFP.