One problem is that body temp will change slightly, but pretty regularly, due to a number of reasons, but still be "normal" (normal can vary from person to person). If you need to monitor your body temp on a regular basis, digital thermometers are very portable and durable. If you need to have a rapid check, there are some that read the temp by sticking it (the thermometer that is!) in your ear and will give you a reading in a second or two, but they are not quite as accurate as an oral thermometer.
Just curious, but why do you need to monitor your temp often? Are you trying to see if it changes under varying conditions?