Hi H.Charles,
I’m certainly happy to help with “how” to choose but there are too many unknowns, variables, and personal preferences involved for anyone to make a specific recommendation for a mattress based on specs (either your daughter’s or a mattress) or “theory at a distance” (see mattress firmness/comfort levels in post #2 here).
The first place to start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that you will need to make the best possible choice for your daughter and know how and why to avoid the worst ones.
There is more about the most important parts of the “value” of a mattress purchase in post #13 here but outside of PPP (Posture and alignment, Pressure relief, and Personal preferences) a mattress is only as good as the quality and durability of the materials inside it. Unfortunately most of the mainstream manufacturers use lower quality materials in the comfort layers of their mattresses which are the weak link of most mattresses and when the foam materials soften or break down it leads to the type of visible or virtual impressions or soft spots that are affecting your daughter. The support core of a mattress (such as the innersprings) are rarely the reason that these issues happen. The way to prevent this from happening is to make sure that you know the type and quality of all the layers in any mattress you purchase (see this article) so you can make sure any mattress you consider uses high quality and durable materials and there are no weak links that will soften and break down prematurely.
Knowing who to buy from and who to avoid and dealing with knowledgeable and experienced manufacturer or retailers who will provide you with all the information you need about the materials inside their mattresses and will give you the type of guidance that can help you make good choices can also be one of the most important parts of a successful mattress purchase (see here and here for a couple of examples)
If you let me know your city or zip code I’d also be happy to let you know about any of the better options or possibilities I’m aware of in your area.
Phoenix