Hi Mark in Texas,
If you are considering building your own mattress I would make sure you’ve read post #15 here to make sure that you have realistic expectations of success and any cost savings (which you may or may not realize).
The component post here has some sources for covers but which type of cover you choose would depend on the design goals of the mattress and would be a preference issue.
There is more about different types of quilted vs unquilted covers in post #12 here and the posts it links to.
There is more about the different types of fabrics in the reference post about sheets (which would also apply to mattress fabrics) in post #7 here.
Phoenix