Hi scubamom,
You are certainly having your share of issues with your PLB mattresses. These types of issues are one of the reasons that many manufacturers tend to be very cautious with any ultra soft materials in the comfort layers of their mattresses because they will always be less durable than firmer versions of the same material … even with latex. While some degree of impressions doesn’t seem to bother some people … for others it can have a much bigger effect on the loss of comfort and support especially if a mattress is close to the edge of the comfort/support range that is tooo soft for a particular person (see post #2 here). With these types of very soft materials it’s often a better idea too add them to a sleeping system as a topper which can be replaced without having to replace the entire mattress.
As you know if the impressions in your mattress reach 3/4" then you would be eligible for a warranty exchange once again and for the mattress that you purchased from Matt-To-Go they would help you with the warranty claim but a warranty exchange is always frustrating and of course it also involves some costs with shipping as well.
The better options and possibilities I’m aware of in the Corpus Christie area (subject to the guidelines here) are listed in post #4 here and the San Antonio list is in post #2 here.
Phoenix