Font Suggestion: Fira (light weights)
Fira Sans only goes down to 300, but there are actually 200 and 100 weights available. Great for headings.
Didn't know that, I'll add it sometime soon.
Thanks buddy! This is a great project you've started here, the new site is looking good as well.
There are actually quite a few additional weights including a useful "book" weight, which is between regular and light.
TypeKit handles this by having two fonts. One with the typical weights and another with the more unusual ones. It's a compromise, but it works pretty well. I just ported my site over to TypeKit from a hand-rolled Fira set (where "normal" was "book" and "bold" was "medium") without much trouble.
BTW, both Fira Sans & Mono were updated a couple months ago.