Pretty much all of the reupholstered seats I've seen have a resulting "puffiness" to them. Perhaps due to a combination of using a thicker/more supple leather + extra foam material. This is totally subjective and I wouldn't be surprised if most people preferred the look of reupholstered seats - they're not bad, just different in my opinion.

Left: OEM
Right: Restorations (of varying quality)

 

Depends on the shop. I went to a shop recommended by several dealers and one local S2000 dealer. Indeed, they look original. No puffiness like you see in your pictures.

 

Clazzo seat covers are popular. They are diy, and go on top of original leather. So they're deliberately oversize, to fit on top of leather, instead of in place of it, like real, quality replacement covers.

Perhaps the puffy ones you've seen are these Clazzos.