Hi parrothead,
You can see the guidelines I use for memory foam mattresses in post #10 here. Unfortunately the density of the foams that are used by bedinabox don’t meet the criteria I would suggest and this would be particularly important with higher weights. At around 200 lbs or so I would begin to use caution even with 4 lb memory foams.
Easy Rest certainly has some good quality memory foam mattresses that would meet these guidelines but with all mattress purchases it’s important to make sure that you know the details of every layer of the mattress so you know that the specific mattress you are considering would be suitable for you.
A mattress is only as good as the quality of the layers that are inside it. The retailer should be able to provide you with all the details and foam densities of all the layers in the mattress so you can know the quality and make meaningful comparisons with other mattresses. If they don’t have the knowledge or experience to tell you what the specs mean … then if you post them here I’d be happy to provide you with some feedback (although I would also be cautious working with a retailer that didn’t have good knowledge about mattress materials or know the quality of what they were selling).
Phoenix