Hi gcrain,
There are a few other Pure Latex Bliss Dealers in the area as well (you can just put your zip in the store finder on the PLB site). PLB has MAP pricing (minimum advertised pricing) but in most cases they will also go down when you are in the store.
That’s not particularly surprising to me. Most doctors have little knowledge about which mattresses may be most suitable for their patients. The lower back issues point to the need for good alignment which usually means firm enough in the support layers so your hips/pelvis don’t sink in too far. The upper back issues usually point to the need for a little more pressure relief and comfort layers that are too firm may also aggravate the disk issue by allowing too much pressure. All of this will also depend on your body type and sleeping positions so your own careful and objective personal testing using the testing guidelines linked in post #1 here would be especially important and I would make surre that you spend at least 15 minutes on any serious candidate after you are completely relaxed in all the sleeping positions you normally sleep in.
All of the online manufacturers you listed have good quality and value and are very knowledgeable about their mattresses and I would encourage you to have a more extended conversation with each of them on the phone. Zoning can be helpful in unusual circumstances or with more “difficult” body shapes. You can read a little more about zoning in this article and in post #11 here. Some good local testing can be useful guideline for an online purchase.
Phoenix