Hi memo42,
I’m assuming that’s a typo and you mean “any particular mattress” or “anyone who knows” rather than “anyone”! 
As you probably know … this is the subject of a lot of debate and each couple can have their own preferences for the type of mattress that is “best for sex” and it would also depend on many other factors such as the positions you tend to use or how “active” you are so there really isn’t really a consensus about which materials or types of mattress are best.
Having said that … I think it would be fair to say that slow response materials such as memory foam are probably the “least favorite” material for sex for a majority of people because they don’t have any resilience and it’s more difficult to develop a rhythm and it’s not as supportive for knees and elbows that are bearing more weight as more resilient materials (see post #2 here).
In the end though … it’s really a matter of personal preference because what may work “best” for one couple may be very different for what works best for a different couple.
Comforters would also be a matter of personal preference and of course the conditions in your bedroom but there is some information in this topic and this topic and this topic and in post #24 and onwards here and this topic that may be helpful and this article has some very useful comparisons and information as well.
Phoenix