I bought mine online using a local website. You can use a regular thermometer, but 2 decimal points allows you to detect smaller changes. If you're not going to get a basal thermometer (2dp) then get a new normal thermometer or new batteries. They don't recommend you use a mercury thermometer either. A little tip, get one with a back light if you can. You can buy them online from AliExpress but just search locally.
I use Fertility Friend app (FF). You enter your data (temp, OPK, CM, BD etc) and it will plot your ovulation when it detects it. If you pay and get the subscription, it does all sorts of algorithms with your data. But the free version is sufficient. You need to enter two forms of data (i.e. temp, OPK or CM) in order for FF to identify ovulation
To temp you need to have at least 3 hours of continuous sleep. So if you wake in the night often, it might not work too well for you. You need to also try to do your temp every day at the same time. I have an alarm at 6.30am every morning. If you miss one date, don't get 3 hours of continuous sleep or take it too late or too early then it's not the end of the world. If you take it too late or too early, put the time in FF (and make sure you set the time you usually take your temp in the settings) and it will take that into account and adjust your temperature accordingly. But missing one or two dates every month is not the end of the world, you should still be able to see patterns.
You can take your temperature orally or vaginally, but you must be consistent and can't change it throughout the month. I find orally is easier, but vaginally will give you more consistent results.
It is also important that you take your temperature straight away when you wake up. Don't have a drink of water, go to the toilet or move around the bed too much. If you sleep with your mouth open, close it for a few minutes and lie still. Then take your temperature.
So overall you should see the following with your temperatures-
During your period - temps are typically low, but may be slightly erratic.
Before ovulation - temps are low
Day before ovulation - may or may not see a small dip
Day after ovulation - temp rises, may be slow or quick rise
After ovulation - temp stays up
If pregnant - temp stays up
If AF is on its way - temp drops.
I guess the other important thing about temping is that it won't let you know when to BD, but it will confirm whether ovulation has taken place or not.
I hope that helps
