Thanks for such a detailed write-up, your questions are really good ones that a lot of people overlook when mattress shopping.
On your foam density concerns: you’re right to be cautious. Even with hand tufting, a 1.35 lb poly quilt foam or 1.45 lb memory foam in the quilt layer will be the first to show wear. Tufting helps anchor layers but won’t make low-density foam last. The deeper comfort and support layers matter more for long-term durability.
On the S&F Reserve Medium: the 3.75 lb Indulge foam is close enough to 4 lb that you won’t notice a huge durability difference. The bigger risk is actually the low-density quilt foam. The “gel foam” listed is likely gel-infused poly foam, gel can be added to any foam type, so the missing word “memory” is probably intentional, not an error.
On Talalay vs Dunlop: Dunlop is more stable and dense, making it better suited for support cores. Posh+Lavish’s approach, Dunlop core with Talalay comfort layer, is actually considered the gold standard in latex construction.
On adjustable base testing: always test flat first. An inclined position offloads pressure differently and can hide support issues. Get your flat assessment done, then test inclined if needed.
Given your history with no-return policies, Denver Mattress’s sleep trial is the safer bet. If you’re ever curious how pocket sprung construction compares, Super Beds offers a helpful range their mattress collection is worth browsing, and the is a good example of how pocket spring density translates to support and durability. Useful context when comparing specs across brands.