Think "Posh Tour", Darryl.
That military-grade positioning was developed over a long time in an effort to reduce tension in the body and likelihood of injury.
Actually it was introduced to me as the way to ensure the neck stays stable in the most ergonomic playing position for fretting precision.
The fretting hand has no other duties than putting the fingers where they belong, and the optimum ability to place the thumb on the back of the neck and the tips of the fingers on the fretted strings.
Any other position results in less than ideal neck stability and thus a loss of precision.
It was deemed so important by my very first instructor that the entire first lesson was devoted to nothing else but how to hold the guitar.
The classical position also allows for the picking hand's forearm to rest on the lower bout at the perfect position so each finger is positioned over the appropriate string. Again, that hand has then no other work than to move the fingers and wrist where appropriate.
Yes it's a little tougher with dreadnaughts.
The next best position is standing, as Walrus mentioned.
If the guitar's neck heavy then a way to keep it stable at the best angle is required.
I'd use something to keep the strap from sliding around on my shoulder.
Spread your legs to accommodate the lower bout (having your right leg angle a bit downward and your left leg angle a bit upward assists, here).
Actually this is where the footrest comes in.
Personally that was one element that never worked for me, they're never stable enough, and they set up at an angle that's counterproductive for my needs at least.
But some sort of "pedestal"' for the left foot to keep the left leg a little higher than the right is required.
The best thing I've found is a Rubbermaid stepstool (see my avatar), but it's still not quite perfect.
Before I found that I used a large block of wood.
I like to keep the left leg "braced" by resting the tips of my toes on the pedestal and pulling the left foot in closer to me than the right foot.
Here's the ideal:
The guitar should be able to rest with the neck at the ideal 45 degree angle in the cradle formed by your legs and torso without you even using your hands.
It'll work for classical guitar 'cause the neck's light enough.
If you're trying to convert from years of playing lying back on the couch with guitar's neck held "level" across you body, it might not be so easy.