Flat footed folks!

Hi all! My flat feet never really bothered me until recently.. when I walk for too long in the wrong shoes, my knees hurt terribly by the end and my legs ache like a mofo.

Anyone with flat feet out there who can recommend a specific shoe brand that might help? I usually opt for sandals and got a pair of Olukais, but I'm in need for better ones and a pair of athletic shoes for walking.

Thanks! :)