Hi mamabear,
I would keep in mind that the design of a mattress and its ability to keep your spine in alignment is much more important for back issues than the materials that are used. Any material can be too thick or soft in the comfort layers especially and cause back issues. With back issues … good spinal alignment in all your sleeping positions is particularly important which means careful and objective mattress testing using the testing guidelines in post #1 here becomes even more important than usual.
The main problem with most mattresses isn’t so much that a material actually wears out as much as it softens under the heavier parts of the body which results in the loss of comfort and support. With higher weights then it becomes more important to use more durable materials and to avoid comfort layers which are more than “just enough” in terms of thickness and softness or the risk of foam softening and breakdown would be higher. A good generic guideline would be to use 5 lb memory foam, 1.8 lb polyfoam (or 1.5 lb in a two sided mattress), or latex in the comfort layers. I would be cautious about using lower quality materials than these in the comfort layers especially except perhaps in smaller amounts (around an inch or so or less). There is more about the factors that are involved in the relative durability and useful life of a mattress in post #4 here.
There is more hype than substance about gel foams in the market although there is “some” truth to the claims. In most cases … depending on the specifics of the gel foam … they can have a small effect when you are first going to sleep but once temperatures equalize then any further effect is minimal. Moisture wicking and ventilation is the biggest factor in temperature regulation over the course of the night. You can read more about the many factors that combine together and contribute to temperature regulation in a mattress in post #2 here.
Aerus is a breathable memory foam but it comes in different densities and I would be cautious with 4 lb memory foam with higher weights and I would also want to know the density of the support layer below the Aerus memory foam as well.
Some of the better quality/value online memory foam options I’m aware of are listed in post #12 here but I would always keep in mind that durability is only part of the picture and that it’s even more important that a mattress is suitable for your specific needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). A mattress that wasn’t suitable for you and you can’t sleep on would have little value to you no matter what it’s quality or “value” otherwise. Your budget is low for a good quality memory foam mattress weth any significant amount of higher quality memory foam although the size you’re looking for would also make some difference (king size would be more costly than queen).
A mattress is only as good as the quality of its construction and materials regardless of which brand is on the label so it’s always more important to know the quality of the materials in your mattress than the brand. Some of the better manufacturers across the country are also local or regional so they may not be available across the country. If you let me know your city or zip code I’d be happy to let you know of some of the better options or possibilities I’m aware of in your area.
If you follow the steps in the guideline post I linked it will help you make the best possible choices in terms of the type of materials and the quality, durability, and value of your mattress.
Phoenix