Hi,
I'm going to be in a similar position having just bought a Kindle. I thought that maybe you could use the Amazon Currency Converter to be automatically billed in GBP but it appears that this isn't available for digital products?
I'm going to get a Post Office credit card which doesn't charge a commission for overseas purchases. Check out the credit card / overseas spending section on the moneysupermarket site.
http://www.moneysupermarket.com/cred...seas-spending/