Hi sonicfox,
A small amount of foam, even 1", especially in the uppermost layer of a mattress, will have an impact on the overall comfort. For slight changes in plushness, it is common for a 1" to 2" latex topper to be used.
That of course varies upon the individual, the thickness of the latex and the ILD of the latex. In general, Talalay is a bit more “buoyant” feeling. Dunlop has an initial softer feel, but tends to “firm up” (has a higher compression modulus) a bit more as it is compressed.
Of course the feel of these products does depend on the surface upon which they are placed, and as you mentioned the sheets and the mattress pad or protector. Unless you have a chance to try any of these toppers out in person, I would make sure that you become familiar with any return/exchange policies of any topper you purchase just in case it doesn’t work out as well as you had hoped.
There are some suggestions for selecting a topper in post #2 here, and in that post as you scroll down there will be a link for some better online sources for topers of which I am aware.
Let us know about your progress!
Phoenix