This is probably the most frequently asked question we got about topper pads in general, and we go over this in detail on our topper pad page. Whether to go with a 2" or 3" thickness, whether it's memory foam, latex, gel foam, or conventional polyurethane foam.
First, I should explain why I never recommended a thinner or thicker topper pad than 3"inches. A thinner, 1" topper pad really didn't provide enough cushion, and if you felt that your mattress was so firm as to need a 4" topper, I felt people were better off spending the money on a new mattress that wasn't so firm rather than trying to fix it with a topper pad. Of course it depends upon what kind of material you are talking about, too. For example, for most people of typical height and weight, we advise 3" almost all across the board. If you are over 145 lbs, definitely opt for a higher density material such as 4lb memory foam, vs. less dense 3lb, which tends to bottom out, especially if you were to buy a 2" thick pad. For latex, a medium firm (not soft) 3" pad is generally the sweet spot, and will do the job for most people. Also, latex can be pretty heavy, and it tears easily when tossed around, so keep that in mind.
Choosing the right topper pad is also a direct function of what is wrong with the mattress you have bought the topper for, so say if you are trying to soften up a crazy firm bed, go with 3" of something on the medium side, not too soft or too firm. So for those with a mattress that was just a bit softer, or bottomed out too much, you definitely want to go a tad firmer so you don't collapse into the mattress. Topper pads usually do the trick, too. With a return rate of only 2 - 3%, our 2" toppers are a solid gamble on salvaging a mattress until you are ready to buy a new one.
Also, these days, keep in mind that memory foam, especially, does not sleep as hot as they used to, since the latest generation memory foam offers much better air flow than solder more dense memory foams. So when you are shopping around, you might want to ask if the memory foam used in that topper pad is a latest generation memory foam offering this greater air flow.
These latest generation memory foams (usually contains a gel component) are a tad more expensive, though, but in my experience they are worth it.