Go to the gym, lift weights and then spend the next 2-3 days with sore thighs, back, chest and arm muscles.
And then do it all over again..... 
Once your body gets used to the exercise, as long as you do it regular enough (like exercise each muscle group twice a week), there's less muscle soreness, and what's there doesn't bother you because you're just kind of used to it. And being a man, you should be easily able to cope with some delayed onset muscle soreness, just like women can, ffs.
What happens when we age - if we don't exercise - is muscle and tendon imbalances (and muscle reduction). It's why you see middle-aged folk in a kind of hunched position, from hours spent sitting on their arses from driving, sitting at a desk, or watching tv (Kyphosis) . Or they walk funny. We've got a local window cleaner who looks like he's spent his life sitting on a horse he walks that strangely.
So muscles and tendons aren't as they should be which means the joints they support don't move properly. Add to that some repetitive stresses on a daily basis and it's just a recipe for trouble. Strength training helps prevent all that kind of stuff.
Forget the mattress and get a gym membership.