Harmonica, I really love those smoking slippers -- they are gorgeous. In your photo they almost look blush, but they seem like a very versatile neutral and feel fresher to me than the wedge.
Do they stay on your feet better than the ballet flat does?
My one reservation is that they seem a bit more polished/ minimal than your typical style, but your style may be moving in a new direction, and I recognize that these would be only one element of your outfit anyway. Plus, I assume they are mostly for work? (Your work capsule is more polished from what I recall and includes modern classics.)
As for the shoes falling off your feet, you are in good company. We've had a bunch of threads about this over the years. I can't wear ballet flats, full stop. And can't wear almost ANY low vamp shoe -- heck, I can't even manage a smoking slipper! This is because my heels are probably a double A width (very narrow) while my forefoot is a normal B width. I need a last that's especially designed for this. None of the inserts that are supposed to help with this actually solve the problem for me. So I simply have to adapt my style for my fit issue. Flats are worse than wedges (I have higher arches and insteps, too, and the wedge means more of the shoe is in actual contact with my foot -- the incline is right). But even heels and wedges can fly off my feet.
My main solution? Booties in cool weather. Sandals in warmer weather. It's not perfect, and sometimes I long to wear a pretty, leg lengthening pump, but I've only ever found a couple that will stay on. I hoard those two pairs whether their toe shape is "in" or "out."
Ecco is a good brand to try. One or two of their low vamp styles have worked for me over the years. Not every shoe, however.