Give these people a try Adam :
https://www.tyreleader.co.uk/
Remember that with tyres, brake pads and other things designed to wear as part of their function in life, you can't keep it original for long, even if fitting the OEM parts. As such, go with the correct size and a brand you are comfortable with. Also look at the reviews for the tyre you're considering, with particular attention to those from your area or the area in which you mostly drive. Road surfaces can (and do!) vary across the country and what gets brilliant reviews in one are won't fair so well in another. For example, Pirelli around the west midlands are gets poor reviews but around the eastern counties gets good reviews. Having driven in those areas in the same car with the same tyres, i can say the reviews are justified but are in fact down to the roads being different.
I recently fitted a set of Maxxis Primetra tyres on my S Type as they were (on paper at least) the closest i could find to Pirelli P6000 tyres, the OE fitment on mine. I have to say i'm not disappointed! Very good tyres with excellent grip and quiet too. The (very) old P6000s that were on the front of mine nearly caused an incident with a telegraph pole because they had gone hard with age and lost much of their grip.
As a point of interest, they were bought online and none needed any balance weights at all when fitted.