Get a New 3DS; the price difference isn't really substantial and you might as well have the additional features. Plus the New 3DS has Xenoblade Chronicles 3D as an exclusive, and you need to experience that if you haven't already in my opinion and you're a fan of JRPGs.
Anyways. machomuu has already outlined the details in differences, so I'll skip that. Being in the UK myself, I miiight be able to help out. I'd advise against the special edition XLs; they're extremely expensive and most of them don't come with games. In fact, I think only the Monster Hunter 4 Ultimate and Majora's Mask ones do.
GAME have a fairly good deal on right now for a White N3DS XL with three Zelda games and, whilst Triforce Heroes is nothing to write home about, the other two are pretty good. The adaptor is a nice bonus, too. Plus reward card points. If you already shop at GAME, it's a nice bonus.
Amazon UK have a lot of deals on New 3DS bundles, but they're from marketplace sellers and I wouldn't recommend them personally. You can pick up a white New 3DS for about £120 or so, so use that as a base price - it'd be cheaper to get the console and game separately than buying the bundle in most cases.
Honestly, I'd suggest getting a white model if that's what you want and then buying the games separately; it'll work out cheaper. Plus they'll be physical copies rather than digital pre-installs. Generally better.