If you had not already stopped the mini-pill, we would have advised you to continue, since a woman’s cycles typically return to normal after about two months.
Fertility Awareness Method is most effective when its practitioners have trained with a professional FAM educator. If you plan to rely on this method for six months, we recommend that you seek out such training. The educator would help you time immersion accordingly. Taking temperature is not a problem on Shabbat with a mercury thermometer in this situation. The thermometer should preferably be shaken down before Shabbat. Writing the temperature down would not be permitted until Motzaei Shabbat. Techniques could be discussed with an FAM professional.
You might also consider using spermicide. The diaphragm is another option, although more halachically controversial. Our site follows the position that the diaphragm is permissible as a contraceptive method, and may even be preferred in some cases, such as when there are untoward side-effects like prolonged staining.
As we state in the article, there are different approaches to the question of immersion when relations will be delayed. Strictly speaking, a couple can decide not to have relations on mikveh night, especially if the alternative of delaying immersion might lead them to be less scrupulous in keeping the laws of niddah. (In this case, the woman would not immerse on Shabbat.) Some rabbinic authorities allow the woman to immerse for the purposes of physical closeness without intercourse. Others are afraid that this will lead to hotza’at zera lebatalah and recommend that the couple delay mikveh immersion. Spermicide might be an option for mikveh night.
When it comes to family planning, it is important to remember that, even with the advances of modern medicine, we do not have total control. Vesting too much in getting pregnant in one specific month can lead to heartache. There is also the halachic question of whether considerations such as the timing of summer vacation are sufficient grounds for contraception – although FAM is less problematic in this regard.