Great write-up! You've found words to describe your concerns in such detail. I think your problem and its solution are pretty clear from the things you have written. This is going to be long; sorry for all the words.
Your words in red, mine in black.
1. Your weight is on the inside ski (should be on the outside ski).
It's like my downhill ski just slides away from me...so wide that I'm going to topple over and lose my balance.
--When your skis are pointing across the hill, the downhill ski is your outside ski. The outside ski always needs most of your weight on it, more pressure on it (weight and pressure are pretty much the same thing). Skiers need to ski with weight moving from outside ski to outside ski, as if walking from foot to foot. When that outside ski doesn't have your weight on it (or pressure on it), it will lose its grip and slide away. Your stance will widen, and you'll lose your balance.
2. You are probably leaning uphill to edge your skis. This hovers your weight over the inside/uphill ski.
--You don't say you are doing this whole body lean, but it's so common that I'm assuming it's what you are doing. Leaning your body uphill, like the Leaning Tower of Pisa, will indeed edge your skis. But it has a very bad side effect. This lean hovers your body weight over the inside ski. The outside ski gets light and loses its grip.
--Where you hover your body determines where the weight-pressure lands. You need to stop leaning your whole body to edge your skis. Use another way to get your skis edged that doesn't involve an upper body lean.
3. Roll the knees to edge skis instead of leaning uphill.
--Crouch a bit, so both of your knees are more bent than normal. Then "roll" both knees sideways, uphill, to the inside of the turn. The knee movement will tilt the lower legs, and it will tilt your boots which are clamped onto your lower legs, and it will tilt your skis which are clamped onto your boots. Rolling the knees will edge the skis just as well as leaning the whole body. It will allow you to avoid leaning your upper body.
--While rolling the knees, keep your head and shoulders, and your whole torso, upright, vertical, instead of leaning sideways.
4. You are probably "leaning in" when your skis are pointing downhill too. Roll the knees to edge the skis through the whole turn so you can keep torso upright instead of leaning.
--You don't say anything about this, but if you are using a whole body lean to edge your skis at the bottom of the turn, you are probably using it for the whole turn. Do you lean sideways to get skis edged and make a turn happen? This whole body lean does work to edge the skis, but it hovers your body over the inside ski and unweights the outside ski. Weight-pressure needs to be on that outside ski through the whole turn. Roll the knees to edge the skis instead. Keep torso upright, vertical, instead of leaning sideways.
5. You are pushing out and away on the downhill ski to "pressure" it harder. But pushing never works.
My instructor has emphasized the importance of really putting pressure on the downhill ski, but I never think I'm doing it hard enough I guess?
--Where you hover your upper body, head and shoulders, determines where the weight/pressure goes. Pushing doesn't work; it breaks the ski away from its grip. Stop trying to add pressure to the outside ski. Just stop. You are pushing it out and away, breaking any grip it might have had. If you are leaning your body to edge the skis, and pushing on the outside ski, that's two things that are keeping it from gripping.
--Solution: keep torso upright, not leaning sideways, so your body weight is not over the inside ski, and stop pushing on that outside ski. That's all you need to do, because....
6. Turning will direct your weight and the pressure to the outside ski. Centrifugal force is your friend.
--When you make a turn, centrifugal force will move a lot of pressure/body weight to that outside ski, as long as you are not leaning in. You do not ever need to "add" pressure or "put" it onto the outside ski. It goes there, if you allow it. Where you hover your upper body determines how effective this is.
7. Your mind wants to control where the weight goes by looking at the skis (looking doesn't tell you where the weight or pressure is).
I can't seem to visualize where the pressure goes. I end up not looking far ahead and ski with my head down looking at my skis
--Feeling where the weight/pressure is will tell you whether the outside ski has more weight on it than the inside ski. Eyes don't work for this. Give them something else to do so they keep busy and stay out of this weight/pressure thing.
--Look down the hill where you are going. The farther you look, the better. You can even choose a visual target to ski towards, and lock your eyes on it. When your eyes are busy looking at something, this will free up your mind to feel, sense, where the weight is under your feet.
--These two things happen on two channels that can run simultaneously in your head - vision, and feeling sensations.
--Notice whether the inside foot or outside foot has more pressure beneath it. Get torso more upright to move more pressure to the outside foot. You may even need to lean your head and shoulders directly over the outside ski, so that the "nose-drip-line" (your nose drips in the cold, right?) falls onto or outside, beyond the outside ski.
--Once you notice your weight is on the outside ski with the channel of your mind that feels and senses pressure, notice whether the heel or the ball-of-foot has more pressure under it. You need pressure to be equal beneath both, definitely not more under the heel. Bend forward at the ankle to move more weight off the heel and toward the ball-of-foot if necessary.
8. Keeping torso upright means keeping it laterally upright.
A misunderstanding is possible with this directive. There's lateral uprightness, as in, not leaning sideways. Then there's fore-aft uprightness. I do not mean keep torso upright like a tree fore-aft wise. That will put you in the back seat. Your body as a whole unit, from feet to head, needs to lean forward over the skis, so your body weight does not hover over the tails of the skis. Why? Because the bindings are behind the center of the skis. The key to doing this is bending forward at the ankles.
