I steam skim milk almost exclusively. While I've been able to consistently make sweet-tasting microfoam with no visible bubbles, it's challenging to get the texture exactly right for art. Too little stretching, and you can't draw at all. Too much stretching and the milk comes out in big white blops. There seems to be a very narrow window where the product is just right for drawing, and it's hard to hit that window every time. I suspect this may be due to the milk and foam separating more quickly than with 1%, 2% or whole milk. Only when you get the amount of stretching perfectly right and thoroughly incorporate the foam can you draw decent latte art.

One trick I've learned is to adjust the resting time based on the amount of stretching. If I stretch too little, I let the pitcher sit a little longer. If I stretch too much, I let it sit for less time.

It's important to swirl the milk vigorously before pouring. If I stretched and textured correctly, it'll get shiny and the consistency will be like wet paint: entirely liquid, but creamy with no visible bubbles. If a blob of foam is visible in the center when I swirl, then I know I stretched too much. If I pour at that point, the blob will come out right at the beginning and sit on top of the crema. I can hold back the foam with a spoon, which allows milk to run out and fill the cup first, and if the foam isn't too terribly thick I can pour art with it at the end. But more often than not, the foam is too thick and a blob of pure white will come out at the end of the pour and sit on top of the crema. Can't draw decent art with it, but it tastes good!

I would say you're probably stretching the skim milk too much and not incorporating it enough. One thing to try is a very short and gentle stretch (just a few seconds), followed by a longer spin where you get a good whirlpool or standing wave going. Another thing to try is to reduce the steam temperature (pressure) if your machine lets you do that. You can also experiment with pouring from different heights and adjusting the rate of pour. If the milk is too thick, pouring faster and/or from a greater height may force more of the foam down under the crema.

As for soy milk, I've only tried it a couple of times and didn't even get the texture right for drinkability. I've read posts here that suggest you need to stop at a much lower temperature with soy milk.