Hi Strumbelina,
While I certainly can’t tell you what to do because I can’t feel what you are feeling or see you on the mattress (and I would pay much more attention to what the people at Parklane are suggesting because they know their own mattresses better than I do, are right there and can listen to you in “real time”, can have a more detailed conversation with you than is possible on a forum, and can see you in person on the mattress) … I can make a few quick comments.
If you are having back pain it’s usually an indication of an alignment issue somewhere in the general area of the pain. While there are many possible reasons that are not possible to determine for certain without seeing you or knowing more information than a forum can provide … the most likely possibility is that the mattress may be “almost right” but just a little bit too soft so you are sinking down a little too far before your pelvis is “stopped” and stretching muscles or ligaments too much or some part of your muscloskeletal system is not in its neutral alignment. This could mean a comfort layer that needs to be a little thinner or firmer or a support layer that needs to be a bit firmer. In either case if this turns out to be the issue they could give you good advice about which mattress would have the best odds of working for you (although I would not tend to make an exchange quite this quickly so you can see if there is any improvement still to come). As you mentioned for someone that is very light then thinner layers of softer foam including memory foam can have a bigger effect as far as how far your heavier parts are sinking down.
I can also tell you that it will take up to 90 days for a mattress to break in and for you to go through any adjustments to a new sleeping surface although this mostly happens in the first 30 days (and it sounds like this has already made a difference for you).
I would be careful with this because it may be a matter of the type of components or materials as much as the overall firmness and just “where” it needs to be firmer (or even softer) just as much as the firmness of the layers. If you go too firm then you may introduce other issues. “Blanket” or more generalized solutions such as “just get something firmer” can often cause more issues than they solve. There are many technical ways to help solve some of these issues connected with larger weight differentials, especially if a couple sleeps close together (see post #2 here for some of the basic concepts), but rather than get into all the complexities of it and turn you into a mattress designer … the best way to know is for both of you to test the mattress together in the same way you sleep. I know it may be a bit embarrasing to “snuggle up” in a mattress showroom for 15 minutes or more (although it could be fun :)) but it’s much better to be a little embarrased than to have years of discomfort by choosing a mattress that doesn’t “work” for you. Couples should always test mattresses together in the way they usually sleep together before buying anything.
You can read about the many different factors that affect sleeping temperature in post #2 here and in post #29 here. as you mentioned the Aurora has 2" of memory foam on top which could be part of the issue (memory foam is more insulating than latex for example and you sink into it more) but your mattress protector (see post #89 here) and sheets and anything else in between you and the mattress and your bedding could also be playing a role in this as well as the softness of the mattress (you sink in further into softer mattresses which means there is more foam insulation around you).
What type of mattress protector do you have and what type of sheets?
Latex won’t generally be as warm as memory foam although the top foam in the mattress isn’t the only factor and the mattress ticking and quilting, the mattress protector, and your sheets and bedding will all have a combined effect on temperature. latex also comes in softer versions so if you do decide to go in this direction then you would likely do best with a mattress that has similar pressure relieving qualities for you (the cushiness you are mentioning) as the Aurora even though the "feel’ will be different. It’s quite possible that yo are quite close to what you need and that either a little longer adjustment or a mattress with just a little bit less “cush” would likely do the trick both from a pain/discomfort point of view and a temperature point of view.
Phoenix