Owning an RR will definitely make you want warranties on anything you ever buy again. Least reliable product ever made in my experience. I'm sure you probably know the shoe size of the service desk teams you've been in there so often!
Warranties for Porsches roughly fall into 3 categories as below:-
Official Porsche Warranty - same as your RR. Extendable to 15 years and can be restored if lapsed subject to a 111 point check at your OPC once you have owned the car for 3 months.
Independents that advertise in the Porsche dealers section on here - lots offer their own very well regarded warranties with them carrying out the work.
Others...basically anything from a general car dealer with the limited
Insurance backed "same warranty for any car" warranty offering.
All have their place.
Getting the car independently inspected is always advised as it's much more thorough than the Porsche warranty inspection.
If it's a private sale and the car has no warranty, ask the seller to have the car 111 point inspected and an Official Porsche Warranty added. This saves the 3 month clause. If they won't allow an independent or Porsche inspection go find a different car, there are plenty out there.
If buying at an OPC you should get 2 years on top of whatever the car already has on it.
The independents advertising on here each have their own cover periods. All are very approachable.
Most OPCs are helpful if you go see the service guys and ask if a car has anything outside of the standard work. Call the ones that did the minor and major service as not all franchises share full details.
Sorry the above is a bit high level, but the question covers a lot....good luck with the search.
991.1 S cars are not that old yet but a few known minor problems include a brake peddle bush that fails resulting in excessive brake peddle travel , fuel flap mechanism that fails, and coolent solenoids that go iffy. All simple fixes under warranty and don't affect all cars.