I want to share with something that changed my life a couple of years ago. I had been sleeping on [namebrand] mattress for just about 5 years. It was good, but the 5 years had taken its toll. I went mattress shopping and tested the big brands and was budgeting for something around $2,000. It seemed excessive but a healthy night's sleep is important to a great day.
For months I read reviews, compared brands and model differences between stores and was getting more and more uncomfortable in my aging mattress. So, I jumped on Amazon and found a $280 12-inch foam mattress just to get me through a couple of months. It came in a small-ish square box and looked ridiculous after unpacking.
Three years later and it's just as comfortable -- I don't need to replace it but a wallet-friendly price of $250 I just might. Even if I replaced it every year it would cost less than keeping that $2,000 mattress.
If your back is bothering or you've noticed some sag in your mattress, I urge you to try it out. Regardless, if you've been sleeping on a mattress for 5 years it is definitely time to start shopping around.