Hi jaystang.
Welcome to our Mattress Forum. 
Sorry to hear about the analysis paralysis! You’re certainly not the first (nor the last) person to find yourself in this stage of mattress shopping.
While there are too many unknowns, variables, and personal preferences involved for anyone to predict which mattress would be the best match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) based on specs or “theory at a distance” (see mattress firmness/comfort levels in post #2 here) … if your back issues are being caused or aggravated by your mattress (which seems to be somewhat likely because it goes away when you have been up for a while) the odds are high that you could find a mattress that will be a much better “match” for you.
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 with how to make the most suitable choice … and know how and why to avoid the worst ones.
There is also more about the most common “symptoms” that people may experience on a mattress in post #2 here that may help you identify why the mattresses you have chosen weren’t working well for you. The most common cause of lower back pain is an alignment issue from a mattress that either has a support core that is too soft or comfort layers (or toppers) that are too thick/soft for your body type or sleeping positions but a mattress that is too firm and doesn’t provide good support under the recessed parts of your body (such as the small of your back) can also lead to lower back pain.
The most important “requirement” for any mattress purchase regardless of any back issues is always to make sure that it provides good alignment in all your sleeping positions.
There is more about primary and secondary support and their relationship to pressure relief and firmness in post #4 here and in post #2 here that may help you visualize what good support and alignment “looks like”.
There is also more about the different ways to buy a mattress and how to minimize the risks involved in each of them if you aren’t confident that a particular mattress is a good match for you in terms of PPP in post #2 here that may also be helpful.
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I feel my first step is to narrow down to either full latex, inner box spring, or some type of hybrid. Given my back conditions described, should I be leaning one direction or the other
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A hybrid is going to retain the traditional “bounce” of an innerspring mattress and also sleeps slightly cooler as the spring allow for better airflow. An all foam configuration is great if you’re looking for motion isolation and the ability to easily swap out layers to customize the feel.
Many of our Trusted Members offer great sleep trials with ease of exchanges and/or returns (obviously varies by policy and company). Many of them are also happy to help you choose something from their inventory that they feel will be your best fit based on what you know you like, your height/weight and your pain points (like you’ve shared here). The difference between a brand like SleepEZ and Saatva is going to boil down to quality of materials, where materials are sourced, brands of materials (like innersprings), and transparency in terms of quality/durability of materials.
I hope this helps!
NikkiTMU