First, do you have a good mattress (not old or saggy.....)
If you have a good mattress that is too firm for you, then a topper might help.
This is the one we bought...
It is excellent...
And, believe me TWO inches is enough!!!
www.absolutecomfortonsale.com/memoryfoammattresstopper.htm
Unfortunately, the mattress that we bought was not as firm as I had thought... so, together, they were TOO soft... This enabled our bodies to sink too much, and not stay supported in alignment...
It is a fine line to get softness and comfort with strong back support!!!!!
So, we sold our nearly brand new expensive topper.
This one is patented, top of the line, COOL comfort.
It does not get hot...
However, we felt that as we layed on it and it warmed up with body heat, we sank down into a body-impression.. or 'hole'. Others have had this exact same concern/issue. Maybe it comes down to personal preference... But, I thought it felt like sleeping in a mattress that suffered from sagging or body-impression wear.
To be honest, if I were ordering a topper today, I would NOT order a memory foam... I would most DEFINITELY go for a quality Latex topper.
This web-site offers top quality Latex toppers as well.