As far as flats, the two I pack frequently don't have great insoles but they're pretty comfy. The first are
Rothy's - they're woven, washable, with a removable insole which helps if you go sockless a lot and need to launder your footwear! I worked in a hospital so the washable part was important to me, and they were comfortable enough for all day wear plus pack like nothing. The second, which are not woven but the leather is super pliable, are these
flats from Everlane which are versatile and comfy enough to be worn all day. I have a few pair of Fitflop ballet flats also, but they're more clunky than I like. Allbirds' wool woven flat that packs well, but support there is lacking and they look almost childish to me. I've almost purchased
these flats as I have some of their loafers, and the quilted lining is quite comfortable, but like a previous poster mentioned, I'm finding that flats are less comfy than they used to be and am moving towards a low wedge or heel or a nice tennis shoe (Paul Green or Hoff are my favorites)
Here's a side by side comparison of some of those shoes, which sometimes helps -
top to bottom - fit flop, allbirds, everlane, rothy's, birdies.
bottoms