Hi Mitzi.
You are most welcome! 
Good to see that you gained a bit more clarity and that you narrow it down to a quality topper to add a bit more softens to your tight-top firm pocket-coil marshall mattress and mitigate the pressure points that you and your husband experience.
It seems that are heading in the right direction and asking the right questions. Since every layer and component in a mattress can affect the feel and performance of every other layer and the mattress “as a whole” and how you perceive and interact with it, now that you decided on the best surface comfort material you do best with it may be helpful to find out a little more about your current mattress.
I was trying to find out what is the overall height of your existing mattress, the Dunlop latex ILD/firmness, and the height of each of the individual component used in their mattress from marshals site but their product “Specs” tab does not function. You may want to reach out to them to find out information listed here so that you can better assess what combo has the best chance to work for you and your husband’s given you. You did not list your specific stats but in your first post you’ve mentioned that you are “fairly average (or slightly under) weight for our height/age” so depending on your existing mattress comfort layer you can go both directions. Typically low BMIs generally do best with softer and thinner toppers and higher BMIs do best with thicker and firmer.
In terms of Talalay vs Dunlop selection, it depends on how much the layer gets compressed under your weight when sleeping on your mattress. Generally, Dunlop starts off softer and (at compression levels past 25%) ends up firmer than Talalay. Generally, as most sleepers will compress a topper past 25% and Dunlop tends to feel firmer than Talalay of the same ILD for most sleepers. There is more detail about this and about the differences between Talalay and Dunlop in post #7 here.
I hope this information pushes you a notch further into selecting the right topper material for your particular needs.
Phoenix