Hi Cassandra,
Sorry you’ve had so much trouble finding a comfortable mattress; remember any mattress you choose will be based on your Stats (height, BMI, sleeping position(s) and any underlying health conditions) and your PPP (Posture & alignment, Pressure relief, and Personal preferences).
You might want to get back to basics and take a look at the Mattress Shopping Tutorial as well as the Mattress Specifications You Need To Know compared to the Mattress Durability Guidelines to see how long specific materials will hold up over time.
Mattresses are such a subjective purchase, no one can tell you what type of mattress or what firmness will work best for you. You are on the right track, noting which materials and firmnesses are not comfortable. Latex, for example, has a particular feel, and not everyone enjoys it. Certainly, if you find one of the ‘Major Brands’ that you like, and go into it with the awareness the durability may not be great, but it’s within your budget, go for it! Realizing a memory foam or polyfoam mattress of unknown density of specifications isn’t going to last for decades is part and parcel of being an ‘informed consumer’. Also as your body profile changes over time, there’s no telling how you may feel when you next need to replace your mattress, and as well there may be additional options in your area when theta time comes…as long as there is a decent ‘sleep trial’ period, you can get an idea if the mattress you choose will be suitable for you.
I wish you success on your new mattress journey, and please feel free to post an update with your final choice and your experiences with it!
~ Basilio