Hi levander,
If you are heavier and prefer firmer I would probably tend to go one higher yet to 32 or so (28 can be as soft for someone who is heavier as 19 or 24 would be for someone who is lighter).
The advantage of BB is that they have a good return policy for their toppers so you can try them with less risk.
At the moment yes (the lists on the forum are an ongoing project but I included Atlanta and the surrounding area in my research). there are some others in post #5 here that may involve a bit more research into what they carry and their level of knowledge and experience but that are also close to you.
They are the result of a combination of a lot of time consuming effort into deep google searches (usually a minimum of 50 pages deep), many other public sites that have various lists, my knowledge of the products and transparency of various manufacturers (deciding which to exclude and which to pursue further), analysis of the websites I encounter and the mattresses they carry, many phone calls to talk with the stores or manufacturers I encounter or know about, and anything else that may turn up a good option in a particular area. All of this goes into my own “database” where I keep my notes of what I find out over time. There isn’t an online database that I use which has this type of “vetted” information (which doesn’t exist to my knowledge) but it’s mostly just time, effort, and talking to people.
The drawbacks of a comfort layer that is too thick/soft are that your heavier pelvis will sink down too far before it is “stopped” by the firmer layers underneath it. This either affects the curvature of the spine itself or tilts the pelvis and pelvic tilt is one of the main factors that can affect and control the natural curvature of the lumbar spine. The comfort layer thickness includes the topper and any softer materials that are already in your mattress because they will both be part of how far your heavier pelvis is “allowed” to sink down into the mattress. This is why an optimal topper thickness depends on the type of mattress it is going on and the thickness and softness of the upper layers that are already part of it. The more soft / thick layers are already in your mattress the less you would need to add in terms of topper thickness. This is why it’s usually better to use experiential guidelines that are more subjective (a little, a fair bit, a lot etc) because this bypasses the need to use theory which can be useful as a generic guideline to understand the concepts involved but can’t be specific to any particular person because of all the unknowns and variables involved that make each of us different from each other.
I also added one more paragraph to the guidelines you linked which is …
Phoenix