I don’t know about vagus nerve reset, but two things that have a calming effect on me that is similar to box breathing and swimming, and that help me sleep, are lying on an acupressure mat and listening to the right sort of audio book. I do not do them at the same time, as I do not want to actually fall asleep on the pressure mat.
The acupressure mat is for any time, daytime or bedtime, but I always need a blanket over me to fully relax into the experience. The audio book is exclusively for sleep. It has to be unexciting, but not actually boring. It has to be either something that I know well or that does not have any complex narrative, so that I do not stay alert FOMO. I never listen to the same books when driving!
The effect of both of these is to distract both the conscious and unconscious mind from the need to stay awake. My focus is drawn to the sensations on my back, or to the gentle story, and I forget to stay alert.
The mat and the speaker to go under my pillow cost less than £15 each. Audiobooks are free from the library, and there are also many suitable websites.