I shifted my LED from discrete to RGB WS2812 ones, because I realised i may need more I/0 Pins for other uses. 

I also figured out that the discrete LED's cannot provide for a good range of illumination i was hoping for, without resorting to PWM. 

I had experience using the WS2812B LED's and I liked them a lot, but my only worry was their standby current draw when they are not lit. Each LED can draw about 1mA from the Battery when it is not on, thereby wasting power when it serves no purpose. 

Even when the Attiny85 was sleeping, the current draw of the DS18b20 and the WS2812LED strip of 8 LED's was about 40mA, which was a big problem area. 

There was an idea. I switched on the LED and the Ds18b20 sensor using a Logic Level mosfet. 

I set my eyes on the AO3416 Mosfet which has a low Rds(on) of 22mohm when the Vgs was 1.8v. This mosfet was a perfect choice to put in my circuit and try. 

I managed to lower the standby power need from 40mA to under 1uA by using the Mosfet. I did gain a little on time, because once the power to the LED was cut off, it has to be reinitialized and that took some time to happen. 

The tactile button in the above image is used to wake up the Attiny85 from deep sleep and start measuring the temperature. 

Overall, I was happy with the whole circuit and decided it was time to design a PCB for the whole circuit.