Do you get cramping under your feet when doing other activities sometimes too like running or sth? 'Cause if that's the case, maybe you need supportive footbeds like the podotherapeutic ones. Could be that your feet are cramping because they need more support. I need those in my daily life but with skiing i defo also need to put them in my skishoes in order not to die of cramp, and they can also help your boots to fit better, so that you can put your boots less tight which could cause the pain on your arches. Maybe thicker socks could actually help? And some boots have inner shoes you can heat up in the oven and then fit them to your foot, maybe that's also possible with yours?