I was a little nervous about purchasing a mattress online. So I wrote down the specs of the mattress and went to a local mattress store. Found the exact mattress (different name, but identical specs). It was firm, which is what we were looking for.
The salesman at the mattress store where I tried it out in person warned us that if we were coming off of a worn mattress, then we would experience a few nights of discomfort (because our bodies would need to adjust to the firmness). These were his exact words, "The 13.75 coil gauge springs are going to feel like they are pushing back at you until your body adjusts). From day 1, my wife slept like a baby! I on the hand... slept miserably! I was actually ready to send it back until my wife reminded me of what the salesman said. Sure enough, I felt like the springs were fighting with me!!! But needless to say, by day 3, I was out like a light!
I tell you this to warn you, give your body time to adjust (especially if you are coming off of an old mattress) and you will not regret it!
We have been sleeping on it for a month and there are no signs of sagging at all!