Hi psimmond,
There is no way for me (or anyone) to know this with any certainty until you’ve actually slept on it because it will depend on the specifics of your mattress and on “how much” additional pressure relief you need (which is somewhat subjective). 2" would be an “average” choice in the range of a “little to a fair bit” of additional pressure relief and if that sounds reasonable to you and you are choosing a topper that is somewhere in a soft range then it would seem like a reasonable choice … assuming that you prefer latex over other types of toppers and you prefer the “feel” of Dunlop vs Talalay (see post #7 here).
The topper guidelines I linked include the guidelines I would use to choose the type, thickness, and firmness for a topper that will have the best chance of success but when you can’t test the combination in person before a purchase then I would make sure that you have a more detailed conversation with any of the suppliers that you are considering so they can help “talk you through” the options they have available and the return or exchange policy may also be a more important part of the “value” for a topper purchase just in case the topper you choose doesn’t work out as well as you hoped for.
Phoenix