Can I please just say...
Should have done it ages ago.
The difference in the restfulness of my sleep is unbelievable. My back doesn't hurt. My hands don't go numb from sleeping on my side. It is SO AMAZINGLY AWESOME!
I didn't really realize just how uncomfortable my old mattress was until I got the new one.
Because I am thoroughly a geek, I even have Visual Displays and Science(ish) Data to back this up. I have a dynamic alarm clock app on my phone, which uses the phone's accelerometer to monitor my movements and wake me up when I'm in a light sleep phase during the half-hour period before the set alarm time. I've tested it with the new mattress, because I thought maybe the foam would prevent it from picking up my movements as well, but it still catches the slightest shift.
Here are a few graphs of my sleep pattern on the old mattress. I picked out some of the better ones - these are nights in late November, after I moved into the new house, when I felt like I got a good night's sleep.
Note that the peaks and valleys are extreme, I completely woke up multiple times a night, and rarely went fully into what the app considers "Deep Sleep". This tells me I was very restless.
Now here's one on the new mattress:
Granted, this was a Friday night, so I slept about an hour longer than on a weekday. Even so...smaller peaks, deeper sleep, and I only completely woke up once.
My "sleep quality" score, which is a combination of length of time in bed and amount of movement (using some mysterious formula), has been consistently 95-100% since getting the new mattress. On the old mattress I considered anything above 85% a triumph, and the average was in the low 70s.
I know this isn't very scientific, but it's pretty cool and there's a definite visual difference in the graphs starting when I got the new mattress. More importantly, I can tell the difference in how I feel in the morning and function during the day.