Hi Looking for a bed,
Just in case you haven’t read it yet … the first place to start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choices … and know how and why to avoid the worst ones.
There is also more information in post #3 here and the posts it links to that will be helpful for those in higher weight ranges.
You can see my thoughts about Bedinabox in post #2 here. I would normally tend to avoid 3 lb memory foam in any weight range but with your much higher weight it would be even more important to use higher quality/density materials in your mattress.
The better options and possibilities I’m aware of in the Northern Virginia area (subject to the guidelines here) are listed in post #2 here.
Phoenix