Hi folks- I bought a new pair of boots (Schnees 13" Hunters with removable liners) back in the spring for an upcoming elk hunt this fall. My normal shoe/boot size is 11.5. I also have narrow feet (B width) and I am flat footed. I had to order a size 12- its also probably a D width. I really like the boots but have decided I need some sort of insert to provide some arch support and help take up some room. What do you recommend? Also should I put it in the liner or underneath it. Any advice is appreciated.