Hi MushroomHunter,
As you probably know … SleepEz is a member of this site which means that I think very highly of the quality and value of their mattresses and their knowledge and service … including their ability to help you choose the most suitable mattress.
There are too many variables to have a “formula” that matches different height/weight, sleeping positions, and preferences to each person and the most effective way to make your choice is by talking to the people who make the mattress and know every small detail of the layering and components (they have several sources) and have the benefit of thousands of customers that they can use as a reference point. There are some general guidelines on the site that can give you some ideas about how different body types, different sleeping positions, and different types of layering and construction can interact together and affect each person’s choices but these are best used as general guidelines and to help you ask better questions and better understand the recommendations they are making and the final choice is always best done in consultation with the manufacturer of the mattress.
Having said that … I would agree that a medium/medium on top is a much safer choice than soft with your height and weight and sleeping style … especially with 100% natural Talalay.
You probably already know this but just in case … make sure you let them know you are a member of the forum so they can give you the 5% discount that the members here receive on a mattress purchase.
I also own the Reverie Deluxe with a 12" latex mattress and it works very well. I think the reverie is among the best values of the adjustable beds. There should also be no problem with your weight combined with the weight of the mattress. The weight capacity of the Reverie printed warranty and documentation is not correct and I have an “official” email from Reverie which you can see in post #3 here which says their adjustable beds will comfortable hold 550 lbs per unit (person and mattress combined).
Phoenix