Most mattresses have about 10 useable years when you buy them. Pillows are good anywhere from 18 months to 2 years. The best answer for "When should we replace our old mattress?" is when you wake up feeling worse than when you went to bed. Sleep is supposed to restore you. You and your body should feel better after a good night sleep.
You spend anywhere from 25-33% of your life asleep in bed. That means that in the next 10 years, you will spend 3 of those years on your mattress (except for that weekend you had to sleep on your cousins futon and had to come in to see your favorite chiropractors right after). With this in mind, it makes sense to invest in a good bed.
In the last few years Tempur-Pedic has really made strides to attempt to reduce the amount of heat their initial mattress models held in. This has made for a more comfortable nights rest. We have seen couples argue less and sleep better after getting a Sleep Number. They have the benefit of having adjustable settings for each side of the bed. Both of these mattresses are good options to look into.
There are also some new companies that are trying to break into the market. They are putting out quality mattresses for around $100 and you can return these beds up to 100 days after purchase. These companies even ship the bed right to your door. Three names to check out would be Casper, Purple and Lessa.
No matter what mattress you buy, you'll want to try it out for at least 30 days. A week in your new mattress isn't enough time to let your body adjust to it. But if you don't like it after 30 days you likely never will.
Hopefully this is helpful. As always, you can ask any doctor at Vallejo Chiropractic for more info when making these decisions.