Hi Talkoran,
While it would probably exist somewhere … I don’t know of a mattress that matches your specific description off the top of my head. I would also be cautious about using criteria for a mattress that are so restrictive that it would exclude almost all of the mattresses that are available in the industry because there could be many mattresses that don’t match your specific criteria that could be a very good choice for you in terms of PPP (Posture and alignment, Pressure relief, and your personal preferences) that use durable materials and are good value as well.
The better options or possibilities I’m aware of in and around the Washington, DC area (subject to making sure that any mattress you are considering meets the quality/value guidelines here) are listed in post #2 here.
That would depend entirely on your risk tolerance, where you are in the range between “I can sleep on anything” and “princess and the pea” and on your confidence that an online purchase will be a good “match” for you in terms of PPP. It would certainly increase the risk if you aren’t here long enough to take advantage of a trial period or the ability to exchange a mattress or an individual layer (in the case of a component mattress). For some people it would be an “acceptable” risk and for some it wouldn’t.
There is more about the pros and cons of an online purchase vs a local purchase in this topic (and the posts it links to at the end of post #3 in the topic) and there is also more information in post #2 here about the different ways to choose the most suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, 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.
If you do decide to purchase a mattress online and you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and “feel” of the materials they are using (fast or slow response, resilience, firmness etc) and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked or other mattresses you are considering that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs and firmness levels to different body types, sleeping positions, and preferences (or to other mattresses that they are familiar with) than anyone else.
Phoenix