Hi Diane37,
While there is no way to know for certain because there can be many underlying causes for any set of “symptoms” … if I had to I would guess that the most likely cause of your symptoms are either a pillow issue or comfort layers that are a little to soft. Either one could produce a “hunched” position that could cause your symptoms (see post #2 here and post #6 here).
Yes … a cover can firm up the mattress to different degrees depending on how well it stretches and allows the contouring of the latex to “come through” and also on its dimensions and how tightly it fits around your layers. I would be a little cautious though because if the underlying issue is that your comfort layers are too thick or soft then a cover may not solve the issue since you could still be sinking in unevenly even though you may not sink in as much overall. I’m not personally familiar with either cover so I can’t compare them so it’s normally a good idea to talk with any supplier you are considering so you can discuss your criteria and they can describe their cover and what you are hoping to accomplish in more specific detail.
Phoenix