This is more a comfortable choice for me. I have narrow feet and I ordered the 8 medium and it fits kind of  loose . I wanted to order the narrow option but it was not available . I was desperate so I bought it .  I hope this helps with my flat feet .  Product was delivered on time .I hope it will last for a very long time since its a bit expensive for orthotic sandals . I hope it helps my knee in the long run !