No idea where you're located, but I would start by taking it to your local automotive upholstery/conv top shops and see what they can suggest. If the tear is in one of the unperforated suade panels, it should be an easier fix than the center perf. sections ... assuming they can match the cashmere color closely.
Also check in to your local Caddy dealer ... they will be able to recommend auto upholstery shops. All of these shops can easily remove the seat, then seat skin and remove the damaged panel to make their pattern and sew a new one back in. Bill
Your dealer will sell you the entire new original replacement cover for about $150 and you can install it yourself. Just make sure you disconnect the battery and wait for about 10 minutes to start disconnecting things, so that you do not blow your air bag.
$115 for a cashmere seat cushion cover @gmpartsdiret.com. About two hours to pull the seat, remove/replace the seat cover and re-install the seat, using common hand tools. Easy fix; did it to my passenger seat two years ago. Patching a leather seat would probably cost even more since you have to pay them to remove/re-install the seat anyway, and would never look like new.