A 100% natural topper would follow suit with a natural mattress and therefore not retain any more heat than it is designed to do. Natural fibres provide the coolest possible sleep surface. A quilted mattress protector depending on the quality of it, should also not have any overheating issues.
As a general rule, to benefit completely from a natural fibre mattress we would always recommend to follow suit and go with a natural fibre topper.
I hope this helps, if you have any further questions please con#’t hesitate to contact the office on 0161 437 4419