In reply to kathrync:
Off the top of my head, both Inov8 and la Sportiva sell basic flat footbeds (various thicknesses) for use in their shoes and boots. Good running/hiking stores will do you, or perhaps call their distributors and/or boot repair people?
For skiing, I'm pretty sure you don't actually need an insole at all; you can just use the boots. If you want a bit of extra warmth, then I feel sure I've seen insulating flat beds from eg. Sidas in some places?