Hi hiddenspring,
Itās good to see you are asking good questions and doing good research 
The read first post I linked earlier has a link to a list of the members here that sell online and there is a wide range of latex mattresses available through them that have many different designs, features, and options. All of them are knowledgeable and provide good quality, value, and service and like all the members here (along with many other sources across the country) I wouldnāt hesitate to purchase any of their mattresses depending on which of the many tradeoffs involved in any mattress purchase are among the many parts of your own personal value equation that may be most important to you. This thread and the links it includes also has more about the pros and cons of an online vs a local purchase.
The OMF latex mattresses are also good quality and value and there are no obvious weak links in the mattress in terms of durability (the guideline I normally use for lower quality materials in the comfort layers is āaround an inch or soā or less because it is already soft and any further softening would have little effect on the long term performance or durability of the mattress). If the polyfoam layer was 2.9 lbs it would be exceptionally high quality but I believe its density is much lower. Since these mattresses are two sided they would actually be more durable than an equivalent one sided mattress. The tradeoff for these are that they lack the ability to customize or fine tune the mattress design or layers and if for some reason you wish to make a comfort exchange there is only one other latex option available. I think their exchange policy (see post #4 here) is actually quite reasonable and fair.
The PLB mattresses at Healthy Back use Blended Talalay (not 100% natural) similar to OMF which is a high quality material. As you mentioned they are not in the best value range but they are certainly ābetter than averageā. Their mattresses are very similar to the Pure Latex Bliss mattresses in design and they use the same type of latex (blended Talalay and talalay GL fast response) made by Latex international. If you know the type and blend of latex in a mattress then thatās really all you need to evaluate its quality.
Iām not sure of the specific design or layers of the Restonic mattress you are looking at so I canāt really make any meaningful comments but they are typically also ābetter than averageā value. Their āvalueā also depends on the retailerās selling price which can vary quite a bit. Once you know the specifics of the layering though then itās much easier to make quality and value comparisons with other mattresses you are considering.
You have certainly eliminated most of your worst choices in terms of brand but I would generally suggest that you narrow down your choice to one specific mattress at each retailer or manufacturer you are considering and then you are in a much better position to make final choices based on the specifics of each mattress along with how well each one matches your needs and preferences in terms of PPP and the benefits and options provided by each retailer or manufacturer more than the manufacturer that makes them.
Phoenix
lol)