Hi pcguy,
Welcome to the Mattress Forum! 
Yes, there are many manufacturers who offer customization and component systems on each side of the mattress. Some of the better options of which I am aware would be the members listed in post #21 here who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex and memory foam and other customizable options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
If you do find something that you’re curious about, feel free to let me know and I’ll do my best to answer any more specific questions for you.
Phoenix