Hi Beaudave,
there is a gap between installing tan/brown/cognac interior and just doing an upholstery of your marine velour seats, a gap of something like 6k€ up.
Finding decent original matching side panels, ash trays etc., nearly impossible nowadays.
I recommend to stay with the marine velour, find a good saddler. Fabric is still available in marine, I would not remove the horse hair, take the foam from BMW E??, forgot.
Regards
Thomas