Thanks everyone. I bought my thermometer at my local chemist for $17. They actually had alot to choose from. The assistant didn't know what a BBT was, and I was trying to explain why I needed it, without the rest of the customers hearing me!
I took my temperature for the first time this morning, and added to my FF chart. I was so excited. My youngest daughter saw me doing it, and later she was trying to encourage me to leave the bedroom whilst she stayed for a little bit more sleep. She would have had it in her mouth in no time.