I went back and read your rather thorough review which I hadn’t seen before. Now that I’ve revisited the store, I find I confused myself with their myriad of names.
The two favorites were from the iSeries, not the iComfort. Our list at that store had gotten down to the iSeries Applause Firm and the Celebration firm, both of which have their new Duet Coil system, not foam, as a base.
As noted by you, we will go to the Williston Mattress Depot to see the Boyd and Natura lines, as well as a latex bed. If you have any idea which models would be similar to the Serta beds, shoot away.
One thing I forgot to add is that the Serta retailer will give us a 30% off anything they sell, in addition to the free pillows and 10% they have this month. So given other monetary constraints this year, that does weigh in on the decision.
So this weekend, we’re off to look at the Boyd line and the others they carry.
Addendum.
It’s going to take me longer to research properly than the time I have been allotted to do this (read, hurry up and get us a new bed, NOW). LOL
Now I’ve become hooked on reading you list here https://forum.mattressunderground.com/t/latex-mattress
Of course, having something this large and heavy shipped sight unseen is a bit scary.
We are definitely not wedded to memory foam, so I’ve begun to look at Latex as well.
Given my above likes, could you steer me in some direction as to an equivalent latex mattress? Possibly the best supplier nearer me that does both types. Right now I’m reading the Sleep EZ factory site, and they’re some 2000 miles from me 
Nice site though