Hi kll4,
I don’t have any personal experience with either cover but based on the descriptions there are some differences between them.
As you know the cover from diynaturalbedding has the puddle pad “built in” and you would be sleeping more directly on the wool. The puddle pad can be zipped off to air out in the sun or washed. The side panels and the bottom are an organic cotton twill which is a little stronger than a cotton knit but will also have less stretch (which is less important on the sides and bottom of a cover).
The cover from Sleeponlatex is an organic cotton stretch knit that would be thinner and not as strong as the twill but it will be more stretchy than the cotton twill. The top and side panels can be removed for washing. In the 6" or thicker versions both pieces would be organic cotton as well.
Thicker covers will also protect the latex against oxidation more effectively (see post #3 here and post #3 here)
If you need more specific information about the materials or how they feel then they would be the most reliable source of information about the specifics of their own covers (both of them are knowledgeable and reliable businesses that will give you accurate information) and a more detailed conversation with each of them would be the best way to decide between them.
Phoenix