Hi Coneflower,
Many manufacturers can make custom sizes so it’s always worth asking if they can make a mattress that is size you are interested in even if they don’t list it as one of their standard options.
This would be a preference choice and would depend on the quality and value of the mattresses that are available to you locally compared to the online choices you are considering and how they compare based on all the parts of your personal value equation that are most important to you. There is also more about the pros and cons of local vs online choices in this topic and the other posts it links to (in post #4).
I would keep in mind that with any good quality mattress if you aren’t able to find a relatively large number of people that have had a specific mattress for at least 5 years or more and that also identify their particular body type and sleeping style that online reviews really won’t tell you much if anything about the durability or useful life of a mattress that uses good quality materials that would be relative to your own personal experience. If there are consistent durability issues that show up in reviews sooner than that then it would be because of lower quality and less durable materials in the mattress that would be relatively easy for any “informed consumer” to identify and avoid without needing to read or wait for reviews. Even if you are able to find enough long term reviews on a mattress that talk about durability over a period of many years by the time they are written then it’s quite likely that the same mattress would no longer be available for sale anyway.
In terms of durability … a mattress is only as good as its construction and the quality and durability of the materials and components inside it (regardless of the name of the manufacturer on the label) and the most reliable way to assess the durability of a mattress or to identify any weak links in the design is by using the quality/durability guidelines in post #4 here.
A mattress that would be a durable choice for one person and that could last them for many years may also not last nearly as long for someone else (in some cases even a few years or less) depending on the many variables that can be involved. There is also much more detailed information about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here as well.
If you let me know your city or zip code I’d also be happy to let you know about any of the better options or possibilities I’m aware of in your area as well.
Phoenix