There already is a great way to get temperature readings using the DHT which is already supported using the Humidity sensor type. However, you may want to try using temperature probes for more extreme conditions like under water. These sensors use the Onewire bus and you need to be sure to enable support for that in the pi.
The Onewire bus will return an object of all items on the bus keyed by their address containing their data. An important note with the temperature sensor using the Onewire bus is that it can be buggy when running with other sensors. At this point support is buggy for this sensor type.
Temperature
[Object]
{
temp1: [float],
temp2: [float]
...
}