Hi AndyC79.
Welcome to our Mattress Forum! 
Thank you for providing your stats and your details in such a well-organized post. It seems that you are well ahead as you have made good progress on your DIY adventure.
Good to see that you did plenty of initial research and that you are putting some safe fails in place for both options you are considering by “looking at expanding ticking so i can add layers if needed.” Keep in mind that the final veto will come ultimately from your body’s interaction with the new sleeping system.
At your BMI a (11") thick mattress is enough to meet all your needs in terms of support/comfort. Both your options have very good chances of working well for you. It is good to see that accounted for extreme differences in sleeping profile (stomach/side sleeping). You’ve been wise to choose a comfort layer that is a little thinner than your “deepest” sleeping position would normally require (typically side sleeping) and then choose a support layer underneath that helps you to sink in a little extra when you need it. A middle layer or “transition layer” can be especially useful for those who sleep in multiple positions and it can help you to sink in enough to help with pressure relief and also help keep you from sinking down too far and causing back issues. This said see my Note* a little lower on the page.
For your wife’s stomach sleeping position you may wish to review the guidelines in this Sleep Positions Article so that she avoids hyperextension in a swayback position that can cause back issues.
[QUOTE] My spouse sleeps hot I am considering latex over coils to help with airflow. Will a 6" coil base greatly help with cooling and airflow vs a full latex core?
[/QUOTE]
While the upper layers of a mattress are the most significant part of temperature and moisture regulation as it relates to the sleeper, the airflow and ventilation will occur from all sides of the mattress including the deeper support components. A hybrid latex mattress that is using a pocket coil core which is one of the most breathable types of cores… followed by latex which is also the most breathable and “temperature neutral” of all the different types of foam materials. Latex allows for more airflow than any other foam and when changing positions on the mattress the air will be moved in and out like within an accordion. As the coils are at least 5" down into the mattress and much further away from your skin, they will have a lesser impact on temperature regulation than the comfort/transition layers.
There are many variables involved in the sleeping temperature including the type of mattress protector and the sheets and bedding that you use (which in many cases can have just as significant an effect on temperature as the type of foam in a mattress) and on where you are in the “oven to iceberg” range and because there is no standardized testing for temperature regulation with different combinations of materials … there is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here.
In very general terms … the layers and components of a sleeping system that are closer to your skin will have a bigger effect on airflow and temperature regulation than layers and components that are further away from your skin and softer mattresses will tend to be more “insulating” and for some people can sleep warmer than firmer versions of the same material.
[QUOTE] Sleep Style 20% Side - 80% Back
Wife will occasionally rest on her stomach, or we’ll be on our side from tossing and turning.
My current mattress is giving me lower back, hip pain from what feels like pelvic tilt. My butt sits lower than my shoulders and sits lower than my lower back. [/QUOTE]
Judging by the percentage of side sleeping (20%) and the “tossing and turning” you experience it may be that you switch to your side only temporarily when the body feels discomfort due to the pains you are experiencing. It would be useful if you could remember your sleep position history when your mattress was not sagging. Were you sleeping on your sides as well? If yes, what percentage.
Note* As your current mattress gives you Lower Back/Hip Pain due to misalignment your body is probably trying to compensate and makes you “toss and turn” onto your sides to give you a relatively good night’s sleep. As you get a more supportive mattress that keeps your spine in neutral alignment for the course of the night, you may find that you’ll sleep less and less on your side which is another variable that you may wish to take into account.
As you are both combination sleepers and your wife is a partial stomach sleeper (which needs the firmest comfort option ) you may wish to consider a side to side split construction for your mattress.
I hope that information helps you out. I think you’re already on the right track and have a general idea of the types of components you need to look for in your new mattress based on your comments. I’ll look forward to learning about your progress and of course any other questions you might have.
Phoenix