I had a nasty cold when checking this post before it was published - my bad. I forgot to include this part:
IMPORTANT: flats with thicker soles and sturdy heels are much more supportive than completely flat flats that feel too close to the ground.
As I responded to Rachy on the blog post this morning, I think a VERY flat and unsupportive flat looks and feels the least nice. You’re after flats with solid soles with at least half to three quarters of an inch in heel height. The feet look more supported that way – to my eye, anyway.
I look for flats that are sturdy on the bottom despite their delicate and refined aesthetic. Flexible soles are important too, but not TOO flexible so that the flat feels floppy.
As far as arch support goes, my low arches can't handle a lot of it. I like GENTLE arch support. Shoes with mega arch support like Danskos, Birkies, Earth and Vionics feel like I have a rock under my foot. I get my support from the soles and sturdy heel. But if you need flats with arch support, you CAN get them.
At the risk of boring you again with my own flat footwear, these are the best examples of what I mean from my footwear capsule.