I haven't read through the whole thread yet, so you may have already covered this.

Have you considered using a gel or foam spermicide? Personally, they irritate me.... but they are a good option nonetheless if you don't have that problem.

Also, if you're considering using a natural method, you should ALWAYS back that up with a condom or spermicide (or diaphragm, or anything really). And if you are planning on using a natural method, you should use more than one... such as temperature and vaginal secretion. It takes a while to get to know your body, but it can be done with a lot of precautions and time. Your body temperature can fluctuate for many reasons, and infections can cause your secretions to be "off" just for example.

Good luck... I'm in a similar situation with my husband. We're pretty sure we don't want kids, so he wants a vasectomy. That would be a huge relief for me. Plus, you can store frozen sperm for years, right? In all honesty, we actually feel it would be more responsible to adopt a child in need instead of have our own. But, his mother would disown us if we did any of that. She's already upset that we don't have kids, and that I had a miscarriage.