I agree the guy at maplins was talking out of his proverbial!
But, wireless N is not a magical answer to wireless range problems, especially not when the devices in question (kindles for example) are only wireless G devices! the nice new wireless N router will be operating in the old wireless G mode to support them and will give no benefit (also the touted range benefits of wireless N are suspect anyhow)
The talktalk guy was on the right tracks to start with, you can keep trying different channels until you find a clear one (there are 13, you've tried 2 so far), but the other obvious answer is to either simply move your router closer to where the wireless devices are being used, or to get a second wireless access point to be used as a repeater to extend your coverage.
I have to be honest though, if you think setting up a router is going to be to hard you've not got too much chance of sorting this out yourself.