Hi beth819,
If you are looking for memory foam or latex that can be returned without risk then WalMart, Costco, and Sams Club are among the best choices.
The Classic Brands is a firm dunlop latex topper so you want to try something firm, this would be a good option to try. A firmer topper won’t generally work well though if it is on top of a mattress that is too soft (I’m not sure what mattress you currently have) because the topper will generally just “bend” into the contours of the softer foam below it which may still cause alignment issues.
Bed Bath and Beyond has the risk of paying for the shipping if you order online (which is fairly nominal for a topper) but I believe they give a full refund at their stores.
The Duralife contains Omalon along with a fairly thick layer of some polyester fiber. They don’t say the firmness level however it is likely quite soft and also thick. The fiber will tend to compress over time but the Omalon is a high quality polyfoam. How suitable this would be depends on the mattress it is going on but if you already have a few inches of soft foam on top of your mattresss then this would be fairly thick and may carry the risk of letting your heavier parts sink in too deeply (which isn’t great for a bulging disc). This would be more of a “fast response” than memory foam and softer than the latex.
The Therapedic topper doesn’t say the type or density of the memory foam they use but it is also fairly thick (3") and so may have a similar risk depending on the mattress that it is being used on. It would be a slow recovery memory foam feel instead of the faster response of the other two choices.
In general a topper works best if it is “just enough” for your needs in combination with the comfort and quilting layers that are in your mattress. Toppers that are too thick and soft can carry the risk of alignment problems.
The Aerus 5 lb 2.5 inch topper at Sams Club can make a good memory foam choice (Aerus is very breathable) with a low risk if you are looking for memory foam. They also carry an Aerus 4 lb topper with the same thickness which would be a bit softer feeling.
Another good option that was discovered by Coventry who is one of our members, may be the Seven Comforts topper sold on Amazon here. It has great value and you can read her review in this thread.
Edit: see post #52 here first if you are considering ordering this topper.
Phoenix