Strings "Feather Bowing"

I'm writing a piece and I want to create a certain effect in the violin sections. It involves making a sort of "airy" sound by having the 1st and 2nds play certain notes, however I want to create the sound by having them barely press down on the bows, so that they create a "whisper" sound.

Is this new? Or is there already a standard symbol or marking for this technique?

I doubt there's a specific marking, however, just marking ppp will automatically cause very little pressure. I'd write something like "with very little bow" and "airy" as an expression marking.

Remember that pressure of the bow directly relates to dynamics and intensity. So you won't have very much dynamic range without sacrificing the tone you're looking for.

It sounds a bit like you're describing flautando - but you might have to back that marking up with some fun dynamics and specific articulations.

On the contrary, the first thing that popped to my mind was sul ponticello. I find it more whispery and airy, despite the tendency to raise the hairs on my back.

I think you are refering to flautando, if you specify sul ponticello will sound a lot more brilliant and I dont know if this is the effect you are looking for, however sul punticello and flautando could work. As you are asking, id write flautando and this will be suficy.