Hi bkim,
Some accurate testing for PPP (Pressure relief, Posture and alignment, and your Personal preferences) along with knowing the types of materials in the mattress (so you know how much they may soften or change in 6 months) can actually be amazingly accurate for the majority of people if you have the help of someone with the knowledge and experience to help you make good choices. This is one of the reasons that testing mattresses in the better factory direct manufacturers or better sleep shops can be so valuable.
Yes … you will need some type of solid non flexing foundation … preferably a metal grid or slatted type (with slats no more than 3" apart as a maximum) to support your mattress. If you have a platform bed with slats then this would also be fine (again if they are no more than 3" apart). There are many options including some that are quite low cost in the foundation thread here.
Both Dunlop and Talalay come in a wide range of firmness levels although Talalay is generally available in softer versions than Dunlop. Either can be softer or firmer than the other depending on the ILD (a measure of softness/firmness) of each. If you are testing Dunlop and Talalay that have the same ILD (firmness level) … then because the Dunlop is higher density and won’t sink in as far … for most people it will feel firmer in an “apples to apples” comparison.
I would consider 36 to be a firm support layer and too firm for the large majority of people for a comfort layer. While I don’t make specific recommendations because there are too many variables in both people and different mattress layerings and components other than the foams that will make a difference … there are some general guidelines based on averages for height and weight here and on different sleeping positions here and how different types of layering will change and affect both of these here. The most accurate way to know what would be suitable for you is either personal testing with the guidance of someone that has good knowledge and experience or by working with a manufacturer online who knows every detail and component of their mattress and how they interact together and has the experience and feedback from a customer base that can help them “fit” your body type, sleeping style, and preferences to their specific mattress.
The Luna protectors and the Protect-A-Bed are both popular and seem to work well but similar types (with a “breathable” waterproof membrane) are widely available and some of these are listed in post #15 here. I would make sure that the fabric was also breathable and would tend to avoid polyester.
With your Malm Bed you won’t need a foundation but you will need one of their slatted bed bases to go with it.
Phoenix