Hi udoknowjac,
The cover of a topper doesn’t need to be the same material as the cover of the mattress no … and the topper and its cover will have a much bigger effect on temperature regulation than the mattress cover because it is closer to your body (see post #2 here about temperature regulation).
Many toppers already have a cover that is included in the topper purchase but for those that don’t the topper guidelines that I linked in post #2 earlier in this thread includes a link to the better topper sources I’m aware of and includes several sources for topper covers as well (to save you scrolling back it’s in post #4 here).
They would certainly be a good quality/value choice for those who prefer gel memory foam over other topper materials. Gel memory foam in general will be a little cooler than some types of regular memory foam … particularly when you are first going to sleep. They can also be a little faster responding and a little less temperature sensitive than “regular” memory foam. There is more about the different types of gel memory foams in post #2 here and there is more about the different cooling technologies that are used with memory foam in post #6 here (one of which is adding gel).
It’s certainly not good to hear this and I’ll try and call them to see what may be happening. (ADDED: I just called them and they answered right away so I’m not sure what may have happened).
Which one would be “better” would depend on the specifics of the topper and which one was the best “match” for the parts of your personal value equation that are most important to you (including their knowledge and experience about their toppers and how they compare to other toppers that are available in the market).
Given that you had previous success with the 3" 4 lb memory foam topper that you are now replacing it makes sense to me that unless you now have a different preference based on testing other types of materials (such as latex) that a similar topper would be a good choice and a gel memory foam topper (or a memory foam topper that has a higher airflow) would have a fairly good chance of success both in terms of PPP as well as helping with the heat issue (if the topper you are considering is either cooler because of the gel or more ventilating than the memory foam topper you are replacing).
Phoenix