Drag yourself to the local store that sells chairs etc.

What is comfortable for one person is torture for another. Somethings have to be purchased hands on.

You can also find steelcase chairs on eBay for reasonable prices. They have all the adjustments and a wide variety of material options.

Tempur is a crazy expensive brand, but does wonders in my case: https://www.amazon.es/Tempur-0855aj-Coj%C3%ADn-Asiento/dp/B001KALM3I Alternatively, the one below has also helped me a lot: https://amzn.eu/d/bUeqLi6 All in all, as someone said earlier, it all varies from one person to another, but there you have my two cents

If your legs are falling asleep it probably means your seat is too high. If you lower it, that should give some relief. As far as a cushion goes, I can't help too much. I had one for my last chair and it worked fine, but I ditched the chair for an Aeron and haven't had any problems at all. As far as I know, any cushion is gonna be just fine. Padding is padding.

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)

I’ve had good results with the cushionlab car-specific one. I know they make a regular one, but the car seat shape works great on the particular mesh chair I have for some reason. Getting out for an occasional walk helps a lot too, even 10 minutes.

I'll say that some chairs are more comfortable than others, but a standing desk is finally what felt the most comfortable for me.