Is British wool better than New Zealand wool and if so why?

I am looking at the Fursdon Bedstead Supreme 1500 & Wool Bedstead Supreme 1700... would the comfort layer of the latter compress down more in time than the Fursdon... also I note that the Vi Spring mattresses made for John Lewis now contain New Zealand wool where as Vi Springs own range contain British Wool...is British wool better if so why? I have spinal and hip problems and a side sleeper only. I would be most grateful for some advice. Regards Mrs J Sparrow