Hi Thinkink,
When you can’t test a mattress in person to make sure that it’s comfortable and suitable for your body type, sleeping positions, and personal preferences (including sleeping temperature) then the most reliable source of guidance is always a more detailed conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests in mind who can help “talk you through” the options they have available based on the information you provide them, any local testing you have done, and the “averages” of other customers that are similar to you. They will know more about helping to “match” their specific mattress designs to different body types, sleeping positions, and preferences, how their mattresses compare in terms of temperature regulation, and which of the firmness and layering options they have available will have the best chance of success than anyone else.
NOTE ADDED JAN, 2016: They have now introduced their new simplified choice mattress which has replaced their previous models and have also become a member of this site.
There is more about the different ways that one mattress can “match” or “approximate” another one in post #9 here but it’s very unlikely that you will find two mattresses that have exactly the same materials, components, and specs so in terms of comfort and PPP (Posture and alignment, Pressure relief, and Personal preferences) the only way to know for certain whether another mattress was comparable would be based on your own personal testing and experience on both of them. Having said that … all of the Novosbed mattresses list a major brand mattress that is widely available that would be comparable that you can use to get a good sense of how they feel. They describe the Aria as being comparable to the Tempurpedic Cloud Supreme and the Harmony as being comparable to the Sealy Optimum Inspiration.
In terms quality and durability … the only way to make meaningful comparisons between two mattresses would be by comparing the type and quality of the materials inside both of them (see this article) but the quality and durability of the materials will have little to do with how a mattress feels or compares to another one. None of their mattresses have any obvious weak links in their design.
All the mattresses you are mentioning are only available online so the only way to “test” them would be in your own home after a purchase but they all have a good trial and return policy as well so the risk of trying them to see if they are a good match for you would be very small if they don’t turn out to be as suitable for you as you hoped for.
Phoenix