Have you tried pixel fonts? Those typically have a size of around 8px (although it is specific to each font). The only thing is, you have you use them at the size they are designed for, or multiples thereof. Sizes outside these ranges look blurry. For example an 8px pixel font looks great at 8px, 16px, 24px etc.
There are a few pixel fonts here that you can try out. Hope this helps!