Hi SteveB,
Welcome … and I’m glad you found us 
While I can certainly help with “how” to choose … It’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
I’m not sure what you’ve read since you found the site but just in case you haven’t read it yet … the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a 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 and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you.
You can see some general comments about what I call “simplified choice mattresses” in general in post #1 here and you can see some more specific comments about the Leesa mattress along with many of the other “simplified choice” online mattresses in post #2 here in the same topic. A forum search on “Leesa” (you can just click the link) will also bring up many more posts with comments and feedback about it as well.
I would be cautious here because the 2" of 3 lb memory foam in the Leesa is a lower quality/density material than the minimums I would generally suggest in the guidelines here and I would consider it to be a potential weak link in the mattress although the 2" of Avena polyfoam above the memory foam would improve the durability of the memory foam somewhat compared to having the same lower density memory foam in the top layer of the mattress.
Outside of the simplified choice list … if you are looking at online options then the mattress shopping tutorial also includes several other links to lists of many of the better online options I’m aware of (in the optional online step) that include many different types and categories of mattresses in a wide range of budgets, firmness levels, and with a range of different return/exchange policies that may also be worth considering.
There may also be some good options available to you locally and if you let me know your city or zip code I’d be happy to let you know about the better options or possibilities I’m aware of in your area.
Phoenix