Hi udoknowjac,
The brand of a mattress or topper is just a label and isn’t nearly as important as the materials inside it so I would focus on the type and quality of the materials rather than the brand. The type of materials in a topper is a personal preference rather than a “better/worse” choice but all materials have higher and lower quality versions that will be more or less durable.
While there is no formula or theory that can predict which topper would work best with each person on any specific mattress (the effect of a topper will depend on the person and on the specifics of the mattress underneath it) … post #2 here and the posts it links to have some guidelines that can help you make the best possible topper choice. It also includes a link to some of the better sources for toppers that I’m aware of.
I’m not sure what “symptoms” you are trying to correct a topper can work well for adding softness and pressure relief for a mattress that is too firm as long as it is still in good condition and doesn’t have any sagging or soft spots. If a mattress is too soft or has developed sags or soft spots over time then at best a topper could be a temporary or partial solution and at worst it could make some issues worse (see post #4 here)
You can read more about the different factors that can affect sleeping temperature in post #2 here. In general memory foam will tend to be less breathable and warmer than other types of foam (polyfoam or latex) although some memory foams tend to be cooler than others (see post #6 here).
Phoenix