Hi Matt ress,
While I can’t tell you which one to choose … I can share the thinking process I would use if it was me making the choice (keeping in mind that your priorities or “personal value equation” may be different from mine).
There are 3 main differences between them which are the cover and quilting, the exchange policy, and the density of the base foam (2.17 lb vs 1.5 lb). These three together with my own more cautious and less risk tolerant approach and my tendency to buy higher quality if I don’t need to “stretch” my budget to do so and can comfortably afford it means that I would personally lean towards the BB Bamboo Bliss.
Having said that … two of these three are non issues for you (unlike me) so for you it would really boil down to the effects of the base foam density.
The difference would normally come into play for body types that are either heavier overall (I tend to use about the low 200 lb range as a very rough guideline) or where the weight distribution or sleeping position of the person concentrates their weight more which would compress the base foam under the heavier parts of the body more deeply. These are the type of people you will often hear about that seem to be tougher on a mattress even though some of them are in lighter weight ranges. Because of your side sleeping positions and your wife’s curvier body type this would probably result in the foam compressing and softening more under her hips/pelvis which would likely mean that there would be some difference in durability between them although it wouldn’t be as significant as it would if you were in a higher weight range. It would also depend on how sensitive either or both of you were to foam softening overall (some people are more on the “I can sleep on anything” end of the range where it wouldn’t make much difference and others are more on the “princess and the pea” end of the range where they are more sensitive to any changes or softening in a mattress).
Since there is really no way to quantify what the specific difference in their useful lifetime would be in “real life” or where the cutoff point would be where you began to notice that you weren’t sleeping quite as well and you were begginning to “tolerate” the mattress a little more … it would really depend on your risk tolerance, your history with mattresses, which end of the “sensitivity” range you think you are, and and on how much a smaller durability difference between them (compared to if you were in a higher weight range) was “worth” to you even without the other benefits that would normally go with the BB Bamboo Bliss.
I believe that smaller differences in sleeping quality over a longer period of time are “worth it” because I think that in a decade or so when you look back on the purchase, a relatively small difference in price (particularly on a yearly basis) will mean less than how well I slept and how long I slept well before the mattress began to lose the comfort and support and I began to “tolerate” it a little more and enjoy it a little less.
While this difference will be less than if you were in a higher weight range, there will be some so it will really depend on how you feel about the pros and cons of each and on how much smaller differences are worth to you. I also think that either one would make a great choice that you wouldn’t “regret” making.
I know this didn’t answer what you were asking specifically (and it can’t really be quantified) but hopefully it will give you some sense of how I would approach it if it was me making the choice.
Phoenix