Temperature-controlled PC cooler speed?

Hello!

I'd like to make a device so the speed of my computer' CPU cooler changes
according to the internal temperature of the CPU (I.e. temp down -> slow down,
temp up -> speed up). This would, AFAIK, help reducing cooler noise on the CPU.
What solutions could I use?

While I'm at it, I'd like to know if I could use a computer fan outside of a
computer motherboard?

Thanks for all help!!