Fertility Awareness Method & BBT

BC don't exist in Thailand (where I'm living until April) and I'm not willing to experiment with their pills because I'm extremely sensitive to hormones. I also tried the Paragard in 2014, but it gave me 8-10 day very painful cycles which lead to anemia (I was also forced to have it removed after 8 months because it traveled up my uterus), so I'm not willing to go the IUD route again either. I've been with my partner 3.5 years and we're open to having kids in the near future, so we thought this was a good opportunity to forego HBC and try FAM. However, I can't find a bbt thermometer, just a regular one. How important is it to have a bbt thermometer, and how much on average does your temperature spike when you've ovulated? Thank you in advance for your help💛