Hi Greyperson.
Welcome to our Mattress Forum. 
Thank you for including all of your statistics! That is very helpful.
Without knowing exactly what you feel on a mattress, it sounds to me that you would have benefitted from a 1" soft layer as opposed to a 3". Despite being a side sleeper, it appears you may benefit from the firm base layer/medium-firm transition layer and then a soft or medium soft comfort layer (based on your needs and preferences, of course). This is a very “rough draft” and can take the form of coils + transition foam layer + comfort foam layer or a base foam + transition foam + comfort foam.
A good starting point for a comfort layer is 2" which allows you to add thickness (or take it away) as you do your configuration testing and/or as your support and alignment needs adjust.There are also a number of forum posts and threads about mattresses and sleepers with larger builds in a forum title search on heavy (you can just click this) will bring up many of them. Some examples include post #2 here and post #2 here and this thread
Ken at Arizona Premium is an excellent resource as well, and would be a great asset in helping you determine your best build.
Hoping this helps you get your DIY journey off the ground!
NikkiTMU