Hi BabyRuth,
I’m not sure what you mean by this and I rarely talk in terms of “should or shouldn’t” because how each person interacts with a mattress is unique.
There are some people who find that some types of memory foam or gel memory foam sleeps warm and they will tend to pay more attention to the many factors that can affect the sleeping temperature of a mattress (see post #2 here and post #6 here). Gel memory foam is one of the technologies that can have some effect on the temperature of your mattress for a while when you go to sleep until temperatures between the body and gel memory foam equalize and the gel memory foam foam … like all foam to different degrees … becomes an insulator beyond that point. There is more about different types of gel foam materials in post #8 here.
So in general terms and to different degrees depending on the type and amount of gel in the memory foam (which most foam manufacturers don’t disclose so the mattress manufacturers can’t disclose this either) the mattress you are looking at already has a “cooling technology” included in it and there are also other things that you can do (such as using different types of mattress protectors or sheets) that may also help to cool down a mattress that sleeps too warm.
Phoenix