I'm also in the UK and the best conditioners are Dove, Aussie or Garnier.
Regarding the split ends, that's probably due to heat damage, so get your split ends cut every now and again. Deep condition your hair every once in a while and it'll start to feel healthier. Also, stop straightening it. Or if you still want to, look for non-heat ways to do so.
Heat damage is quite hard to recover from so I would also get some conditioner spray. I use Aussie Miracle Hair Insurance, it's BRILL, can be bought anywhere in the UK. It conditions and stops frizzing. I started to use it a couple of years ago and it really makes my hair shine.