Designing and building your own mattress can be a lot of fun but can also be quite frustrating and involves a lot more knowledge of how different materials, layers, and components interact than many people suspect. I would normally recommend working closely with a manufacturer who will be able to give good advice about all the different components over using your own knowledge and separate sources to build your mattress but for those who want to forge ahead with their own design anyway … this will provide some options.
Ordering layers separately and where to order would depend on the material you wanted. The foam factory has been fabricating and distributing for more than 30 years a broad range of foam, rubber, sponge and upholstery products that are of good quality and value. If you want to see what you are buying first or talk to someone that has the skill and knowledge to help you make good choices.