There are different types of cushions, and I think this should be the focus.
High density polyurethane foam is commonly used for chairs, mattresses, etc. When used in sufficient thickness (depends on your weight), this foam will conform to your body and be very comfortable. I weigh 165 lbs so about 3” minimum to 5” is better. This foam will rebound from compression for about 2 to 3 years if used for ~10 hours per day. After such use it will have a permanent sag, and should be replaced to retain original comfort.
Memory foam is very comfortable because it is highly conforming, so you will press more deeply into the cushion. And it’s often used in combination with high density polyurethane foam. The thickness will depend on your weight and you might need more because you will compress more. Also, once this foam is compressed, the rebound happens more slowly - about a minute. And this foam will rebound from compression for about as long as high density polyurethane foam, (2 to 3 years if used for ~10 hours per day).
Next is latex foam. There are basically 2 kinds of latex - dunlop and talalay. (You can research that yourself because I’m lazy, and nobody is paying me a fair wage for this report.) Latex is usually made in 3 densities - soft, medium, and firm, and the firmness will depend on whether it’s made by the dunlop or talalay process. Latex will last longer (about 10 years), and cost more. Cushioning comfort depends on what density you choose and there is more variety with latex. For firm support latex is a very good choice.
If you’re still interested in reading this longer than expected report, for which I’m being grossly underpaid, I suggest you consider the information above when choosing new chairs. And you might want to have the cushions replaced on your current chair. Or, you could supplement your current chair with sections of foam or latex, and make a pillow of sorts.
Finally, you might wonder why I know about something so trivial and superfluous as cushions. The answer is simple. I’m lazy! 😀
PS… If anyone is interested in materials used for pillows, and their characteristics, I could write a report for you on that as well. Of course it depends on how lazy I feel, and your willingness to pay a fair wage for my time. 😜