Our daughter uses the potty full-time during the day since she was 1.5 years old.
For awhile she was dry all night.
Nowadays it fluctuates. Two weeks, dry as the desert. Two weeks later, the floodgates open. I'm fairly certain she pees her weight overnight.
We tried up-ing the diaper a size like you did and she's filling that up too!
We tried diaper doublers which just became a pain for me to clean.
I asked her if she remembers feeling as if she needs to pee pee and she said no. I think this is true because she really is a sound sleeper.
We have a two fold tactic now.
When we wake up in the middle of the night for whatever reason, we go in and change her diaper. If it's during the weeks where she is pee-ing alot most of the times it's full. On some nights, we've changed her diaper at most 3 times!
Sometimes, depending on how we are and how she is, we carry her to the bathroom and tell her to go pee pee. She's half asleep and goes!
I don't know what the answer is but I know this is not permanent.
All I can do is offer hugs and let you know you are not alone in this nighttime adventure.