Hi sleepseeker2021.
Welcome to our Mattress Forum. 
Thanks for your appreciation, hopefully, now that you’ve “landed” here on The Mattress Underground, we’ll be able to share some insights, resources, and knowledge that may help you to move forward.
Certainly, a 5 years/4 mattress turnaround can be quite unsettling but it looks like you’ve started to recognize a common thread as it relates to sleeping hot and the comfort issues you’ve experienced.
Most of the mattresses you selected are a combination of memory foam or poly on top of a spring unit or air bladder. While spring is great to use as a mattress core for those who sleep hot, I’d keep in mind that the upper layers of a mattress are the most significant part of temperature and moisture regulation as it relates to the sleeper,
Memory Foam will generally be the least breathable and most insulating of the foam comfort materials, so the temperature can be an issue. Gel memory foams too… are a subgroup of memory foam with similar properties and there is a lot of hype and exaggeration about the cooler, faster response, or the more supportive new generation of “enhanced” memory foams. While there is “some” substance to the claims and cooling gels certainly have some slight cooling benefits (usually temporary when you are first going to sleep until temperatures equalize), there are many other alternative materials and combinations that have similar or better properties such as latex rubber.
Another drawback of a memory foam comfort layer (including gel-infused) that may account for your comfort and pressure points issues is its temperature sensitivity: Viscoelastic foam goes through a transition from elastic to viscous within a certain temperature range. Foams that are more temperature-sensitive will be firmer when they are cooler and softer when they are heated by the body or the environment. Humidity also plays a role here (higher humidity softens it). Memory foams that are less temperature sensitive will tend to have less of a range of softness and firmness. foams that are more temperature-sensitive will be both firmer and softer depending on the degree of softening and transition into viscosity from elasticity.
The latex layer in the CPR may not be the main reason for sleeping hot. Latex in general is the most breathable and “temperature neutral” of all the different types of foam materials but the firmness of a mattress and how much you sink into it can also affect sleeping temperature as well. While it’s also not always possible to track down temperature regulation issues for any particular person on a specific mattress because there are so many variables involved (including your room temperature and humidity, your sheets and bedding and bedclothes, your mattress protector, or any mattress pads you are using, and where you are in the “oven to iceberg” range) and some people can sleep warmer on mattresses that most people are generally fine with … there is more about tracking mattress temperature regulation issues potential causes ~ Post #2 here (at least to the degree possible for a specific mattress) and the posts it links to that may be helpful.
You can read more about the many variables that can affect the temperature of a mattress or sleeping system in post #2 here and the posts it links to that may be helpful. You may also be interested in the information in post #28 about temperature regulation and mattress microclimate.
Some of the factors involved in how warm a mattress sleeps are how closely the foam conforms to your body (the more closely it conforms around you the more insulating it is), how soft or thick the foam in the comfort layers are (the softer/thicker it is the deeper you will sink into the more insulating materials), the type of quilting used in the mattress (natural fibers allow for more airflow and humidity control which translates into better temperature regulation), the type of ticking (cover) used (natural or more breathable fibers such as cotton or viscose or even some of the more breathable synthetics will wick away moisture and ventilate better and humidity control is a key part of temperature control), and on any cooling technologies used in the mattress such as ventilating and moisture-wicking materials, heat conductive materials, or phase change materials.
In addition to this … the mattress protector you choose along with your sheets and other bedding and what you wear when you sleep will also have a significant effect on temperature regulation because they can either add to the insulating effect or to the ventilating and moisture-wicking effect of your mattress. Bedding made from natural fibers or viscose materials (like bamboo) will also tend to be cooler than synthetic fibers and linen sheets along with silk are probably the coolest of all the natural fibers for those where the sleeping temperature is a main priority. In many cases changing the mattress protector, sheets, or bedding to cooler versions can make “enough” of a difference for many people who would otherwise sleep hot on a mattress.
When it comes to mattress recommendations for pressure relief … it is not possible for anyone else to make a choice for you as every person is different and only you can feel what you feel on a mattress. This is why I always suggest, if you haven’t already, to first review different comfort/support needs of the various sleeping positions. The short version: most side sleepers need 2" to 4" of material in the comfort layers. Without an appropriate comfort layer, a side sleeper may experience pressure points during the course of the night and could have symptoms of numbness, soreness, localized redness, or end up tossing and turning all night as your body tries to relieve the pressure.
I’d also take a look over the Mattress Durability Guidelines which will help you identify any weak links in a mattress as far as components are concerned.
You mentioned the buckling column gel and the Purple mattress more than once. Generally, buckling column gel is certainly an interesting material but like any material, some people will do well with it and some won’t. The thing that’s most unusual about it is that it has what could be called a negative compression modulus. Compression modulus is the rate that foam becomes firmer with deeper compression. With buckling column gel instead of getting firmer when you compress it more deeply like foam materials … it starts off firmer when it’s not compressed and gets softer when the columns buckle under pressure.
A DIY is certainly an option and can get a bit complex but it is usually a rewarding option if approached in the spirit of adventure. You’d be able to tweak and adjust the mattress to your liking, and can do a side-by-side split if your partner would prefer a different feel or firmness. If that’s the route you choose to take, there are experts and resources on TMU to help you.
Lastly, but probably the most important piece of advice, is not to make a purchase without having an in-depth conversation with the retailer or manufacturer of the mattress you are considering with regards to your needs, experience, and preferences; you’ll want to be on the lookout for retailers and manufacturers that employ people who are more interested in educating you and fitting you to a mattress than they are in the profits they will make (they understand that profits are a side effect, not a “cause”). They can tell you “why” one mattress may be better than another for your needs and preferences. And, they’ll be the best equipped to tell you whether a certain mattress is a fit for you or if they’d recommend a different mattress.
Let us know how your Naturepedic store visit turned out and if you found something that you like.
Phoenix