Hi Michjjc,
I don’t know of any manufacturers that make mattresses made of sand (and I’m not so sure that many people would buy them if there were) but a buckwheat hull mattress may be somewhat similar. If you are also considering mattresses that are made of more traditional materials then the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort” and PPP that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you.
If you let me know your city or zip code I’d be happy to let you know about the better options or possibilities for retailers or manufacturers I’m aware of in your area (some of the manufacturers may make custom mattresses).
If you are also considering online choices then the mattress shopping tutorial includes several links to lists of many of the better online options I’m aware of (in the optional online step) that include different types and categories of mattresses with different designs, options, firmness levels, prices, and return/exchange policies that may also be worth considering and some of them also make custom mattresses as well.
Phoenix