Hi Joe Cool,
Welcome to the Mattress Forum! 
You may have already found this, but for others who may be viewing this thread, I have some information about motion isolation in post #18 here.
There are so many variables involved in your comparisons that it’s difficult for me to comment to specifically, but I can provide some additional general commentary that may be useful to you.
Starting with edge reinforcement, there are some “all foam” memory foam mattresses that use racetrack or wedge shaped systems in their base foams that do help provide for a firmer edge reinforcement. Specifications are constantly changing from different manufacturers over time, so I don’t have a listing of what brands do or don’t offer edge reinforcement in a memory foam mattress – it is too large of a job for any one person to begin to compile and maintain with any accuracy.
Your assumption of moving to a king and that it would assist with minimizing motion transfer is correct, with all other things being equal, as there is more area to absorb/disburse the movement/energy. There would also be more room for the dogs. :lol:
In comparing a typical memory foam mattress that uses polyfoam for the core versus pocketed springs for the core, there are of course other layers of material that can impact the ability of the mattress to “deaden” movement. While you tried out a few innerspring memory foam beds and found those few particular mattresses unsuitable, there are pocketed spring models available that do offer an extremely “dead” feel. Whether or not these would be suitable for your use would of course come down to careful testing to see if the comfort aligned with your individual preferences. Perhaps there are more knowledgeable members of this site who have searched for and found a product like what you are desiring and they can offer their feedback.
You’ll also want to make sure that you were testing each mattress in the showroom on the same type of foundation and bed frame to standardize your comparisons. The typical metal bed frame under a mattress set is one of the largest culprits in “amplifying” movement, and even the most basic mattress can be made to feel more solid by placing it on top of a very solid platform bed or bed set, as opposed to a “standard” metal bed frame.
Unfortunately, there is no standardization of minimization of motion transfer scale, so I can’t offer more specific guidance than the general things that I’ve listed here and in my linked post.
Also, thank you for your comments in your first post in the other thread.
Phoenix