Cables! They work! Make your bike shift!
I've been using Jagwire Slick Stainless cables for years. I've used sexier (and pricier)PTFE-coated cables (Teflon is one brand name for PTFE) and those cables do perform marginally better. But the Jagwire cables cost a lot less, have provided the same quality on every cable I've bought, hold up well under harsh riding conditions, and I've yet to break one.
I always like to have an extra cable or two around, and this works well.
but you should do yourself a favor and just buy a whole set (brake and shifting).
or buy two!