Hi helpwanted and welcome to the Mattress Underground 
We bought a king-sized Nest Owl in October with Medium latex. It feels super comfortable when I lay down, but sometimes I think it might be a bit too squishy, and I sometimes wake up in the morning with some lower back pain.
Sorry to hear your Nest Owl Medium is not working ideally for you. It’s a solid well built bed, however, remember that any bed you choose will be unique to you both based on your Stats (height, BMI, sleeping position(s) and any underlying health concerns) - thanks for providing those! - and your PPP (Posture and alignment, Pressure relief, and Personal preferences). Different mattress types can have wildly different ‘feels’ for any consumer.
I’m also not sure I like the coils/hybrid aspect of this bed, and we noticed that her side was firmer than my side, even thought we both got the Medium latex. We just switched it to see if it helps my back, but I’m really not a fan of how squishy the coils are, especially at the edges. And there are certain spots where the bed really “gives” too much underneath, like if I sit where my head usually goes, I sink down quite a bit, if that makes sense.
I’m thinking of returning it and picking up a 3-layer all-latex mattress from SleepEZ, but I’m not sure if this is a better or worse option than a hybrid for my weight, height, and sleep preferences. (My wife is way lower maintenance than me, so she doesn’t care what we get)
As you can see by comparing the Mattress Specifications You Need To Know to the Mattress Durability Guidelines, latex is one of the most durable materials you can have in a mattress…and while many consumers enjoy the feel of an innerspring mattress, others don’t, feeling, as you have found, it to feel too ‘squishy’. It’s good your wife is ‘totally open’ to whatever mattress you find comfortable, so you effectively just need to consider data points for your own sleep profile, making things a bit simpler.
As you have had prior back surgery and have a higher BMI you need to consider both your desired firmness in your comfort layer(s) and your support needs; a too-soft comfort layer can allow you to ‘sink’ too far potentially bottoming out on the firmer layers below, which can also cause muscle aches and pains and even alignment issues…you just need to find the ‘sweet spot’ between the two.
An all latex mattress from Trusted Member SleepEZ is a sound plan…as they carry great quality latex mattresses- though if possible you might want to try an all-latex mattress in a local showroom, just to see if you like the feel before committing; @CST also has a great point, as they use a body profile that takes into account the measurements for each sleeper, and they can create a customized modular sleep system which you may find addresses your comfort and specific support needs. They, or any of the Trusted Members of the site will be able to assist you in finding your perfect sleep system. Hoping others chime in with their thoughts as well.
~ Basilio