Sorry for the lack of response in this area; I hope you're in good shape.
The more I've thought about it, the more it seems that having at least a one-off personal instruction session would be of benefit, if only because that's how I learnt it and finding some decent videos would be a stretch, so to speak, not least because I'm way too easily distracted (yeah, OK, my self-discipline is terrible if you want to put it another way!)
So, for a start, some things to look into would include:
pelvic floor exercises
alternating leg lifts
abdominal crunches in combination with one or both of the preceding
These exercises are Pilates-based. One thing that is
crucial is that you pull your abs inwards in this type of exercise. This ensures that you engage the correct muscle groups for core stability; if you allow your abs to bulge outwards this is incorrect.
My partner has a ton of good Pilates floor exercises for this but again, none of it as online resources (we are so old-fashioned, it seems
) but again she emphasises, these exercise must be done correctly which brings me back to my original point about instruction. Pull that belly in!
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli