Hi mccarthd26,
The Christeli Astoria is comparable to the Tempurpedic Contour Signature (which they call firm) , the Novosbed Sonata is comparable to the Sealy Optimum Destiny (which is the firmest of the Optimum Series), and the Novosbed Classic is the equivalent of the Tempurpedic Contour select (which they call extra firm) so all of these would be much firmer than the Tempurpedic Cloud that your in laws are used to sleeping on. You could test the equivalent of each of these to decide which one was closest to the “feel” you were looking for or which one felt the softest to you. If I had to guess at the relative firmness levels (bearing in mind that I haven’t tried any of them) from firmest to softest I would guess the the Classic, the Sonata, and the Astoria.
The Novosbed Sonata uses 4 lb gel memory foam which would be a little less durable than the 5 lb memory foam used in the other two but it’s also softer and since this is a guest mattress this wouldn’t be as significant to me as as how it felt.
With several mattresses that were different in design … a $100 price difference would be insignificant to me compared to the other parts of your personal value equation that may be more important to you and there is no way to “quantify” whether the difference would be worth it based on the cost of the individual materials (which manufacturers don’t disclose) so it along with the pillows would be just part of the things that I would consider as factors in your final choice based on all the parts of your personal value equation that are most important to you.
I would also treat the foundation as a separate purchase that didn’t factor into the mattress choice because all of these can be purchased as a “mattress only” with any suitable foundation and there are similar foundations to the one Christeli sells available as a separate purchase (see the foundation thread here).
I haven’t tried any of the Christeli’s mattresses in person so I can’t speak to the effectiveness of their dual sided option but the separate softness levels on each side would allow you to customize the feel of each side to some degree although the 3" of memory foam and the quilting on top would reduce the amount you would feel it compared to sleeping on the different firmness levels directly.
ADDED: I should also note that Christeli only has an exchange policy and no longer offers a return/refund as an optional add on that you could purchase for an extra $29.95.
Phoenix