UK, Where to buy windows 10 from for pc built? Not OEM version

I ordered all my pc parts to built my first gaming pc, but what is still missing is the operating system. Obviously I'd like to get windows 10, but not an OEM version. Best so far I found was 71£ on Amazon delivered on a usb. Are there better websites to purchase it from? I found a few with very low offers but they were all OEM.