There are others on here with more detailed knowledge about carpets. Have a "search" on Ausmini too.
It is said that the early Cooper S made in Australia had a Feltex carpet which was a coloured and patterned material like underfelt. It was changed shortly afterwards to a special westminister ribbed style.
Have a look at this site:
https://www.ebay.com.au/itm/16496819777 ... Sw145g5P5oThey use Tretford carpet for their mini carpets, as it is as close to the original as is available.
Attachment:
Green Westminister Carpet.jpg
This is a piece of original carpet from a BRG S from under the heel pad. The colour in the photo is hard to see accurately, but looks more like a cross between "Apple" and "Olive" on the colourcard, although "Olive" would be the usual choice.
I bought a length of Bilberry and made my own carpets for a Marine Blue S a few years ago. I had the time and got the satisfaction of doing it but the carpet alone cost over $400 so the AllCarCarpets price would be worth considering.