Anyone have valuable feedback on purchasing a memory foam mattress?

Looking to replace my old bed, Killing our backs! Im searching reviews, brands the types, density, materials and such. Would really value feedback from others who already own one. My husband and I did go out to try them out and see how they feel. We are conflicted on the prices in a box store and online prices, which vary significantly. Nutshell—we dont want to overpay on an item! Thank you!