Hi isabel14. Welcome to the forum. The best battery prices are generally places like walmart. They can tell you exactly what size you require. If I recall it is a group 48/h6 battery for the mk6 tdi. Also know that diesels sound like the battery is dead when cold outside particularly to those new to diesels; if you don't have to jump it, it may be ok. It may be beneficial to have the battery checked, again walmart or any parts store. Definitely stay away from the dealer for a battery IMO.
A 2014 is a mk6 btw, not a mk5 so while we are happy to help you, this is not the right forum. Best of luck.