Hi AustinOski,
I switched your post and the other replies into a new topic of it’s own since it is more about the foundation than the mattress.
The soft would be softer than most people in your weight range would choose based on “averages” and it certainly makes sense that you would be compressing the softer foam layers more which would cause your daughter who is lighter to roll into you.
There is some good information about the 3 most important parts of the “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase to fine tune the mattress or the exchange return options that are available to you).
The most common reason for premature soft spots (virtual impressions) or visible impressions in a mattress (regardless of the price of the mattress) is lower quality materials in the upper comfort layers (a mattress will tend to soften or break down from the top down) but if you follow the suggestions in the quality/durability guidelines here and make sure that a mattress you purchase used higher quality and more durable materials and that it doesn’t have any weak links in the design then it would be reasonable to expect that a mattress (regardless of the price) will have a useful life in the range of 7 - 10 years and if the materials are higher quality and more durable than the minimum guidelines then it would likely be in the upper end of the range and possibly even longer.
I would keep in mind that the price of a mattress isn’t a good indication of how long it will last and there are many mattresses that are in a much higher budget range that use lower quality and less durable materials that will soften and break down much too quickly relative to the price you paid. There are also many mattresses in lower budget ranges that use very low quality materials that may only end up having a useful lifetime that can be measured in months or possibly a few years. The most reliable way to assess the durability and useful life of a mattress relative to different people and other mattresses you are considering … regardless of the price … is based on the quality and durability of the materials and components inside it.
It certainly isn’t an ideal choice. There is more about the different types of support systems that generally work best with different types of mattresses in post #1 here. There is also more about support systems that would be suitable for TheBestMattressEver (or other mattresses that use a similar support core) in this topic as well. In general terms … a foam mattress will do best on a support system that has very little to no flex under the mattress and that has a large enough support surface area and small enough gaps in between the load bearing surfaces to prevent the mattress from sinking or sagging into any gaps in the support system over time.
It may shorten the useful life of the mattress to some degree because of the additional flexing under the mattress (although I don’t know how much) but the biggest issue is that the additional flex may affect the support of the mattress and the ability of your sleeping system to keep you in good alignment over the course of the night. The only way to know this for certain though will be based on your actual sleeping experience.
The coils won’t provide as much cushion as adding a topper because the mattress on top of the coils will absorb most of the weight of the people sleeping on the mattress and if you have a foam mattress that is too firm then I would use a topper instead of adding some additional flex underneath the mattress which you may or may not feel. It could add a little bounce to the mattress but latex is already a very resilient material so this wouldn’t normally be a significant issue and the box spring under the mattress could also add to motion transfer between the sides of the mattress as well.
Phoenix