Hi lilmon,
If the latex is synthetic then it would be Dunlop … probably made by Mountaintop Foam which makes continuous pour Dunlop with either synthetic, natural, or a blend of both.
It would be normal for the soft side of the mattress to feel slightly firmer when you are lying near the middle of the mattress because of the transition between the firmer and softer side. There is more about the pros and cons of a side by side split in post #2 here.
While I can certainly help with “how” to choose … It’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
“Support” is often misunderstood because the goal of a “supportive” mattress is to keep the spine and joints in good alignment and this requires the type of contouring support that allows some parts of the body to sink in more (softer) and some parts of the body to sink in less (firmer) and this will vary on an individual basis based on body type and sleeping style. There is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support/alignment” and “comfort/pressure relief” and “feel” and how they interact together.
Again though … since I can’t feel what you feel or see you on the mattress the only way to know for certain whether any mattress will keep you in good alignment in all of your sleeping positions will be based on your own careful testing or your own personal experience when you sleep on it. Even people in the same weight or BMI range may have different body types, sleeping positions, sensitivities, and preferences so for some people it may be fine and for others it may not be.
Phoenix