Same here! I got a second set to use, because I could not bear to use the first set.
I think the girlie shirts, despite the name, aren't just for kids, but it just means that they are fitted, so they're more flattering. I tend to look like a sack of potatoes in a "normal" shirt, even the M size.

But if the S is really XS like it says on the page, it might be better to go for the M.
About postage, I think it was 10 euro for a longsleeve and a CD a few months ago, to UK. I'm sure it's gone up, as I'm sure I once got a ziphood sent for less than that a few years ago. I think it's probably 10 dollars for something to USA.
I wish they had put a table listing the cost of weights of merch to the different countries...

there used to be one. However, the calculator in the Nightwish shop is not very accurate - it ends up charging you more than the table says.
