Yes the Cloth options were more prevalent in the four seat versions. I would have to go to my reference library (original Buick sales catalog for 1971) to see if that were the case for other styles. I do NOT recall ANY option as for leather.
It depended on specific model and interior level ordered. What year are you talking about specific? GS it was just vinyl 70-72. No cloth available on GS. This is available cloth insert on base Skylark.
I have a 72 skylark split bench w/o arm rest with the exact cloth pattern shown above in green, only mine is blue. Last I checked with Legendary, they don't offer this pattern in blue, which sucks for me because the gs vinyl pattern they offer will look odd with the "x" pattern on door panels. Looks like I may have to go to local upholster for a custon replica $$$$$$ if I want to match! Pretty sure the 68-69 had very different cloth patterns from 70 and then 71-72. I would try Legendary, they are very knowledgeable and helpful. They will offer something suitable for decent price if you're not picky on style. Pretty sure someone on this site will have the period correct brochure for your car if you ask.
SMS fabrics has tons of NOS material but it will cost you dearly. The route you are taking may not be worth it. You will easily overspend the value of the car.
Pretty sure they have what you want https://smsautofabrics.com/collections/1972-buick/model-skylark-350-4-door-sedan
You're right Dave, they want $180/ yard + shipping. I'll probably end up with the gs gtyle skins from Legendary.
I am embarrassed to tell you what I spent for my 71 never to use it. Not one of my wisest decisions. You are making the right choice.