Mattresses have changed a bit in material quality over the past 20 years, particularly with the legacy brands. Most have gone to a one sided mattress approach. There is nothing inherently wrong with a one sided mattress provided they are using better quality foams, fibers, materials, thoughtful design and build, combined with a quality foundation.
I recently had the pleasure of visiting a Saatva store in Winter Park Florida on vacation. Being 6’ 220 and my preference for a firm mattress, both my wife and I liked the Saatva HD, she is 5’4 135, both side sleepers mostly, so we definitely are outside the characteristic of conventional wisdom as it pertains to mattress firmness and sleep position. But for us as we tested it (she was a not so willing participant on vacation, but, she was a trooper, as it was really hot outside and cool in the store.)
The Helix mattress is a nice choice, at your age with a firm support requirement. I would suggest the Helix Plus Elite. The great think with the elite series, if you purchase through an authorized independent retailer, they can order a split internal comfort layer in a king size. With the plus series you get the benefit of a firmer more robust spring support, and with the Elite series, independents can order split internal comfort layers, for each sleeper, and if you dont like a particularly insert, they can swap it out for a different firmness, without sending the entire mattress back.
The Helix Plus Luxe is a slightly less firm version of the of the basic Helix Plus. Like all of the Plus series, they use a firmer 13.5gauge spring support system. The Luxe adds a bit more cushion to the comfort layer over the core Plus. The Elite offers several additional benefits with additional lumbar support and microcoils for additional airflow and contouring.
With their additional improvements added to the upgraded versions in April, this Helix is a nice mattress in this category of mattresses.
Keep in mind your old bed frame may not be ideal. It is important to know what type of base that it is, and the condition it is in. Adjustable bases are an excellent option for a mattress. You dont need to go crazy with features, some basics are acceptable, but you do want the deck to be made with solid bases. Some of the metal grid bases can be problematic for certain mattresses.
You are correct, most do not accept returns on the bases, but regardless of the mattress, a quality base will work on practically any mattress, but always check the specs of the mattress and whether it will accept and adjustable base.
Your observation about testing a mattress for only five minutes is an important one. While high-quality mattresses made with dense foams, durable springs, and premium materials are often a good indicator of longevity and support, a brief showroom test, whether five or even 30 minutes, can’t fully represent long-term comfort. That’s why a trial period or a mattress modification policy is so valuable.
Not every company offers a full trial period, but many that don’t will provide a modification option instead. This allows experienced professionals to assess your comfort concerns and adjust the mattress or topper accordingly. As long as the company has a solid reputation for customer service and follow-through, this can be a perfectly acceptable and effective solution.
Hopefully, this helps the thought process going forward.
Maverick