WAOAW Seat Cushion, Office Chair Cushions for Desk Chairs, Sciatica Car Seat Cushion for Back Coccyx Tailbone Pain Relief, No-Slip Dual-Linings Protects https://www.amazon.com/dp/B08F1XLGB1/ref=cm_sw_r_cp_api_glt_fabc_VA7JR9JBP11QDZ7X9H1B?_encoding=UTF8&psc=1

If you can find a dealer height Gary Platt chair you'll be good for quite a while. If you just need a couple inches of height these types of cushions are great. Just make sure you get one with a non-slip bottom:

https://www.amazon.com/WAOAW-Cushion-Office-Chair-Memory/dp/B08F1XLGB1/

My favorite cards are Faded Spade. Very easy to deal with and durable. Copag are also quite good. KEM have a great reputation but they have a tendency to warp and after they're used for a while they start sticking together.