Buying expensive fans is a bit.. well.. tricky, in that if you are spending loads of £ on fans you should have just bought a better case with better airflow and fans to begin with. Instead of a cheaper case and expensive fans. Still, you've got the case and you're stuck with it.
The Noctua fans mentioned above are an option - but don't buy them through the article link because they are £23 each on that seller. If you buy them from Noctua on Amazon they're only £12.50 ish
Buy Noctua NF-S12B redux-1200 PWM, High Performance Cooling Fan, 4-Pin, 1200 RPM (120mm, Grey) at Amazon.
You could also get less expensive ones like be quiet! Pure Wings that are about £7.50 each or Arctic fans that are typically less than £5 each.
Your case has space for fans at the bottom and on the front at the side. You could get 2 fans, try them in each position, and see what works best.