Hi ryan83,
If you are considering building your own latex mattress I would make sure you’ve read post #15 here and the posts it links to first to make sure you have realistic expectations of success and the costs that may be involved.
The “best” approach to a DIY mattress is a “spirit of adventure” and a willingness to go through some trial and error and where what you learn and the satisfaction that comes from the DIY process itself is more important than any cost savings you may realize (which may or may not turn out to be the case).
If you do decide to go in this direction then post #4 here has some of the better layer and component sources I’m aware of.
Phoenix