Just make sure it is a Basal Body Temperature thermomitor. They can be glass with stuff that rises (they don't use mercury anymore but i don't know what they us in it now) Or you can go digital. Most women like the digital because it beeps when done and some of them even remember your temp in case you forgot to write it down.
My problem is that i dont even know when i ovulate.
My fiance and i are trying for a baby and im on metformin because of lack of periods. I just think that things are not working or i'm doing something wrong.
Good luck.
I went to CVS (a drug store nearly everywhere in the continental US) and bought a CVS Brand basal thermometer which works great, but I was informed by my doc that temping is not always accurate for a minor percentage of women like me. I hope it works for you!