Hi Kelly,
if a video demonstration might help get an overall idea, one place you might find it for free is from Manoj the Yogi's website. He explores a number of different sources, so what is available might not reflect the AYP form of YMK, certainly not the gradual self-paced way of adding the different elements together. As far as I know, he covers many of the practices in the Bihar system, though it depends on what form is taught in which book, and whether he includes it or not. Searching through the book if you can obtain a copy or find it at a library would be a start to determine where in the videos it would likely appear.
Your holding of breath instinctively during pranayama is not entirely part of the instructions, but bordering somewhat more into automatic yoga. The line blurs a little between that and a normal progression of the slowing of breath during pranayama. For easy measuring of self-pacing, YMK cycles are instead suggested for breath retention. I've talked to Christi about this before, and it's been something that came up quite naturally in my practice too that I continue to use and enjoy. I mention this not to make anything seem more complicated, but as a factor for us to also take into account when adding practices steadily. Like this, more options are available to you, whether to continue it for a while longer before adding YMK, following the lessons and not doing it deliberately, or also adding on YMK to an already more intensive (aggressive) pranayama. You'll know what's right for you, and what you're comfortable with.
Do you also use uddiyana (abdomen in and up) and mulabandha/asvini (root lock) during pranayama? I ask because if these are already familiar, and you already do a version of kechari 1 (tongue to upper palate where the soft and hard surfaces meet), YMK would seem a lot simpler.
You simply continue on an inhale cycle of pranayama, but hold the breath and engage those then. Depending on when you use mulabandha/asvini during pranayama, so far it would be identical to what you're already doing.
Now YMK starts, where you ignore sambhavi (eyes to third eye), and instead apply gentle pressure on the eyes, while sealing the nose. That's it for the retention phase.
Static chin lock can be added a little later on, so leave it out for now to keep it simple. It is after the breath reaches brow, and released before breath is released. Fingers simply apply a gentle pressure on the eyes, replacing sambhavi, and this you always hold during both retention and exhale/inhale. The other fingers have to be released or you won't be able to exhale/inhale. The instructions explain the fine details better. Always go with those, since my version has one or two slight modifications (I inhale slightly before starting exhale) and at times it's hard to remember which is official.
