Hi Carrie,
Unfortunately you are in a similar position to many other that have come to the forum and are somewhat caught between a rock and a hard place with a mattress that hasn’t held up or that wasn’t a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and needing to exchange it at a chain store where there aren’t any particularly good quality/value options available to you.
You can also see my thoughts about airbeds in this article.
Post #2 here has more information and suggestions about the two main strategies that you can use that can help you make the best possible choice.
Post #13 here also has more about the most important parts of the “value” of a mattress purchase (or exchange) that can help you make more meaningful comparisons between the options you have available as well.
Phoenix