Hi LackOSleep,
Just phone them and ask if they have their all-latex mattresses on the floor. Not all of their stores will offer it. It will save you a trip.
When you can’t try out a product in person, your next best option is always a detailed phone conversation. I’m glad they were able to offer you some good initial advice.
I don’t remember the density of the polyfoam Selectfoam uses in their mattresses except to say that it is in the higher quality/density range but they are very transparent and will provide them to you when you talk with them. There is more about the different lines of mattresses they make in post #9 here but the Tri-Pedic line uses more traditional TDI memory foam.
My last notes show that the Tripedic line uses “regular” 4 and 5 lb memory foams and the Diamond uses the Tempurpedic Cloud Luxe as a comparable reference point. That may have changed since my last conversation with Selectabed, so you’d want to confirm this with them with a phone call. They’ve always been very helpful with their specifications in the past.
However, if by “feedback” you mean “reviews”, while other people’s comments about the knowledge and service of a particular business can certainly be very helpful … I would always keep in mind once again that you are the only one that can feel what you feel on a mattress and I would be cautious about using anyone else’s suggestions, experiences or reviews on a specific mattress (either positive or negative) or review sites in general as a reliable source of information or guidance about how you will feel on the same mattress or how suitable or how durable a mattress may be for you. In many if not most cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person or even a larger group of people in terms of “comfort”, firmness, and PPP may be completely unsuitable for someone else to sleep on (even if they are in a similar weight range). In other words … reviews or other people’s experiences in general won’t tell you much if anything about the suitability, quality, durability, or “value” of a mattress for any particular person (see post #13 here).
The Selectabed return policy is listed here. They offer 120 days, after which you may opt for a refund or exchange, depending upon the mattress you’ve chosen. It appears that you’d be responsible for return shipping. This policy falls within the range of many online options, so I’m not sure what part of it is severe to you, unless you’re referring to the return shipping fee that you’d potentially have to pay. Shipping is always included in the price of any product, either to or from the manufacturer. Manufacturers with “free” shipping include these costs into the price that everyone pays, effectively subsidizing return shipping of the few that return/exchange an item. Other manufacturers choose to have customers who pay for the retun freight directly and not pass this cost along to everyone. Which method you choose is part of your own PPP.
If you’re looking for other online options to compare, use expertise of the members listed in post #21 here (I linked to this earlier for you in another post) who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex and memory foam and other options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
I’m just glad that you’re feeling better on getting stronger. 
Please keep me updated with your progress.
Phoenix