A bunch of good advice in this thread
I agree totally that a major factor is a decent diaper, and having
confidence in it. You mentioned that you wear Northshore Supremes, a very decent night-time diaper.
One thing that worked for me was timing, and setting a routiine. Barring any major incidents, I change into a fresh diaper in the morning, after I've been up for over an hour, and showered. I change again after work, which is normally when I am wettest. I change the last time right before bed, adding plastic pants/Garywear briefs if I know I've been drinking more than usual. I know from experience that my Northshores can go through multipe MAJOR wettings, so I have confidence that I'll be "covered" throughout the night, even if I wake up multiple times to wet, which is rare.
Lie on your back or front (back is better), and just relax, knowing that it will be okay. The wicking and absorbency on the Northshore Supremes is excellent, so you should have zero concerns about leakage, and you don't get that constant soggy/clammy feel. You DO feel and notice the weight and the swelling, but is not uncomfortable at all. It's important to relax, because if you don't, you'll hold back, and possibly wake up multiple times for smaller,wettings.
If you're still paranoid, you can just use an insert/doubler/stuffer and plastic pants. I've never experienced any issues with leakage with that setup. Of course, an even better option is wearing thick, multi-layered cloth diapers and plastic pants. I've only done that a few times,because I HATE washing diapers, but it the far more secure, and as another poster mentioned, the only way to safely wet while in any position.