Best seat cushion for my mesh desk chair for working from home, for my poor bony butt bones, and my legs don't fall asleep?

Same as you. Trust me when I say this is the best chair I've ever used. 5 years on and still a solid chair.
https://www.staples.com/union-scale-flexfit-hyken-ergonomic-mesh-swivel-task-chair-black-un59460/product_990119

Gaming chairs are scams. Overpriced and just have fancy colors on plywood. Get a solid officechair. They make their chairs sturdy and ready to have someone sit in them for 8 hours a day 5 days a week.

Mesh is another huge +1, this chair keeps you much cooler. People think they want leather or something. No, it gets too hot, and if you're sweaty at all it's sticky, and they don't last well. A solid mesh keeps you cool, supported, and your bony ass can sit comfortably for long periods of time. (Just remember to stand up every once in a while, for health)