The thermistor idea is viable, but not widely used, that's why there are so few "simple" circuits to be found on the web.
It's often true that circuits that have few components are often harder to get working, beginners can be intimidated by the number of parts in a circuit, but in reality, the complexity can yield design s that are more tolerant of part variations, therefore require less fiddling around to get them working.
I would go for something brutally simple.
For example, you could use some simple optical sensors to detect the movement of thin pieces of aluminized mylar film that could be positioned to move easily in the stream of your breath.
You can troubleshoot this system without extensive electronics knowledge, it's all rather intuitive.
It's often true that circuits that have few components are often harder to get working, beginners can be intimidated by the number of parts in a circuit, but in reality, the complexity can yield design s that are more tolerant of part variations, therefore require less fiddling around to get them working.
I would go for something brutally simple.
For example, you could use some simple optical sensors to detect the movement of thin pieces of aluminized mylar film that could be positioned to move easily in the stream of your breath.
You can troubleshoot this system without extensive electronics knowledge, it's all rather intuitive.
