I recently purchased a new mattress and found there is a lot you don't hear about when you buy a mattress. I recommend if there is a local small manufacturer you buy from them. Many of the foam mattresses on the market have so many chemicals in them and the fire retardants they spray on commercial mattresses also have additives that are carcinogenic. I went with a vispring mattress, because they use no chemicals in there treatment and have a lifetime warranty.
I don't think you have to spend a fortune but definitely spend the time asking questions. I also don't like buying mattresses from furniture stores unless you know the mattress is shipped to you from the vendor and not sitting in a musty storage facility. There are still some really great mom and pop shops that make quality mattresses around the country. I'd see if you can find one local to you. Find out whats in the mattress and avoid foam if you really read about foams you'll see they are loaded with chemicals. There is a chain that is not 100% natural but they are very honest and answer questions its called Saatva I found there sales staff very informed and prices reasonable. Unfortunately they didn't have what I was looking for but they have a good product.
Good luck