Why are you not 1.) doing cleans, and 2.) not wearing weightlifting shoes, whose metatarsal straps reinforce your arches?
I have addressed the PC issue elsewhere, and I feel that unless you're doing them you're not doing SS. Heavy squats done in good shoes will not bother your feet, or everybody that squats heavy would have bad feet, and they don't. The fact that yours are already flat make an even stronger case for getting some good shoes. And calf raises may in fact aggravate the situation. I would spend money on shoes instead of orthotics, and I'd also tape my arches before I trained. If I were you.