In reply to Laurie Rogerson: Sounds like the masses have come out to recomend superfeet for someone who just wants a bit of extra padding!
Superfeet are actually quite hard compared to some, if you don't need support then you might be more comfortable with sorbothane double strike or just a plain old gel insole.
If you do want support and cushioning I'd recomend SOLE footbeds, they come in two thicknesses. The black ones are thicker and will give you more padding provided they don't reduce the volume of your boot too much. Unlike the superfeet they mould to your feet, either by warming them in the oven and then wearing them, or just by wearing them in.Having tried both I find the sole ones comfier and more supportive.
A few people have recomended getting prescription orthotics, make sure you get someone decent to make them. The best ones are 3/4 length only and they wont give you the cusioning you need. I've seen dozens of people wearing ones from podiatrists which are totally useless in terms of support and of poor construction. It doesn't sound like you're looking for an orthotic anyway but if you do make sure you get a good physio and don't get fobbed off with a thin bit of foam with a wee wedge built into it.
Ben