Hi mnmeater,
This is hard to know because there are many different versions of memory foam which are difficult to compare outside of personal experience because the feel and response of memory foam changes with humidity, temperature, and time, and will react differently to different people. As a very general comment though I would say if you are talking about the same density memory foam in the same thickness and in the same environment then “probably not” even though your own personal experience is really the only way to tell. If the return policy is good and there is little risk then other memory foam toppers may be worth trying (and experimenting with different thicknesses) to see if it feels softer to you (regardless of how it may feel for someone else).
Your upper body is lighter than the pelvic area of the body and has a larger surface area (on your back) so it will tend to sink in less than the pelvis. While the pillow under your knees will tend to relieve tension in the Lumbar spine … you are also facing issues that may not have an ideal solution until your back is healed.
No … there are very few doctors that have much knowledge of mattress construction as it relates to specific people and they will mostly give very “generic” advice that is not individualized to their patients and based mostly on “what they’ve heard” rather than specific research or study (such as “try a firmer mattress” which has little practical meaning). They are generally no more informed about mattresses than consumers although there are exceptions that may be worth calling at places such as sleep clinics or doctors that specialize in sleep issues.
It probably wouldn’t help much to test the sleep number beds because even if you did discover a solution that seemed to work (and this would mean spending long enough on the mattress to make sure your results reflected your actual sleeping experience) it wouldn’t really be possible to “translate” it into meaningful terms because the sleep number beds can change the firmness of the support layers but use the same materials on top as other mattresses and you can’t change the support layers of your mattress. The only thing worth testing with an airbed would be one where the middle section can be made firmer to see if this helps.
It may be worth considering is a topper that can be “zoned” so that the upper part of the body has softer materials under it and can sink in more and the lower part under the pelvis is firmer. Some examples of these include …
customsleepdesign.com You can talk with Bob who can “split” the topper to make is softer on the upper part and firmer in the lower part.
https://www.flobeds.com/products/linens/mattress-toppers.htm These are shredded latex and there is a zipper to allow you to add or remove latex in different sections to make them firmer or softer.
A google search on “zoned topper” may also turn up some choices (mostly memory foam) but they will involve some trial and error and if you consider any of these I would make sure that the return policy is good if it doesn’t work out for you.
Finally a wool topper may also be worth considering because it can reduce the amount you sink into the foam underneath it and still provide comfort (and temperature regulation) under your upper body. You can talk with some of the manufacturers listed here that make them to see what their thoughts are as it applies to your specific circumstances. One of them even makes a wool topper with a firmer center section. I would keep in mind though that wool tends to be firmer than soft foam … especially when it compresses over time … and once again the return policy may be an important part of a purchase decision to reduce the risk if it doesn’t work out for you.
Phoenix