Hi backtosleep,
I’m sorry your Leesa mattress isn’t working out for you currently, but at least you did have the foresight to choose a product that has a good return policy should things continue to not work out for you as well as you would hope. The Leesa has 2" of Avena 3.65 lb. polyfoam and 2" of 3.0 lb. memory foam on top of a 6" 1.8 lb. polyfoam core. It’s possible that this may not be the preferred componentry, in thick enough quantities, or substantial enough in the comfort layers for your personal preference. And unfortunately, there is no one type of mattress guaranteed to alleviate back pain – I wish there was! 
This would be specific of course to each individual.
The Leesa, like most modern mattresses, only needs to be placed upon a firm and flat surface, and a platform bed would be one surface that generally would suffice. There’s more about appropriate foundations for most modern mattresses in the foundation thread here.
Unfortunately, there are no meaningful specifications listed on the City Mattress web site, or the pranasleep site, for me to make any meaningful comments about the karma moon plush or moon super plush. Both use a pocketed spring unit along with poly foam, but no layerings or densities are provided. There is also no meaningful information about the City Mattress Sequoia Plush on the City Mattress site, so you’d have to contact them for the exact specifications and information listed here (I also linked to this in my reply to one of your posts previously). Once you would have that information about any of these mattresses you could then compare that information to the durability guidelines here.
There is no latex in the Leesa mattress (see the specifications in post #2 here), and there’s no listing of any latex in the three mattresses you mentioned from City Mattress. This is why it’s so important to deal with retailers who are knowledgeable about their products and to acquire complete specifications.
Again, the pranasleep mattresses you mentioned were not latex mattresses. Latex in general will be one of the most durable foam mattress material you can find, and it will show very little loss in compression modulus (support factor) over time.
The mattresses found at City Mattress are mostly the types of brands I usually advise to avoid, as they tend to be less transparent about their materials and tend to use lower quality foams (see the guidelines here along with post #3 here and post #12 here and post #404 here). And the few brands that they offer that do tend to use better materials are in a higher price range and I would make some careful “value comparisons” before considering purchasing those items.
First, in case you haven’t found this already, some of the options or possibilities I’m aware of in and around the Rochester area (subject to making sure that any mattress you are considering meets the quality/value guidelines here ) are listed in post #11 here .
There is more information in post #9 here about the different ways that one mattress can “match” or “approximate” another one. Every layer and component in a mattress (including the cover and any quilting materials) will affect the feel and performance of every other layer and component and the mattress “as a whole” so unless you are able to find another mattress that uses exactly the same type of materials, components, cover and quilting, layer thicknesses, layer firmnesses, and overall design (which would be fairly unlikely) then there really isn’t a reliable way to match one mattress to another one in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your Personal preferences) based on the specifications of the mattresses (even assuming that you can find out all the specifications you would need for both mattresses you are comparing in the first place).
Mattress manufacturers generally try to differentiate their mattress from the mattresses made by other manufacturers and don’t normally try to “match” another mattress that is made by a different manufacturer so unless a manufacturer specifically says in their description of a mattress that one of their mattresses in the same general category is specifically designed to “match” or “approximate” another one in terms of firmness or “feel” and PPP and/or they are very familiar with both mattresses and can provide reliable guidance about how they compare based on the “averages” of a larger group of people that have compared them (different people may have very different opinions about how two mattresses compare) … the only reliable way to know for certain how two mattresses would compare for you in terms of how they “feel” or in terms of firmness or PPP (regardless of anyone else’s opinions of how they compare which may be different from your own) would be based on your own careful testing or actual sleeping experience on both of them.
There are also no “standard” definitions or consensus of opinions for firmness ratings and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress that feels firm for one person can feel like “medium” for someone else or even “soft” for someone else (or vice versa) depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see post #15 here) so different people can also have very different opinions on how two mattresses compare in terms of firmness and some people may rate one mattress as being firmer than another and someone else may rate them the other way around. This is all relative and very subjective and is as much an art as a science.
In other words … the short version of all of this and the “bottom line” is that spending time testing “brand name” mattresses or any mattress where you can’t find out the specifics of the materials and components inside it is mostly wasted because it would be too risky to purchase and it can’t be used as a reference point to purchase another mattress that is “similar”.
I’d first refer you back to my reply to your earlier post and follow the steps outlines in the mattress shopping tutorial and the links I previously provided.
If you wish to look online, you can use the experience and expertise of the members listed in post #21 here who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex and memory foam and other options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
Their detailed knowledge of their mattresses and how they fit with different body types and sleeping positions along with your feedback from local testing, a customer base of many people that they can use as reference points, and any exchange, return, or any options they have available to customize a mattress after a purchase can help lower the risk of an online purchase. These online retailers or manufacturers can also be a good “value reference” for local purchases to make sure that if you are paying a “premium” for a local purchase (in exchange for the kind of “in person” guidance, service, and value that comes with dealing with a local retailer that can help you make more “accurate” choices that you have tested in person) is not too high. They can also inform you of any potential return/exchange polices that they may offer just in case your purchase doesn’t turn out as well as you had hoped.
Phoenix