Yay, I found it! When I searched before I posted, I just put in doubleknit and came up with about a gajillion posts that mention dkweight yarn, nothing on double knitting...
Now I feel silly...I should have kept on sorting through them...
Anyway, if anyone wanted to find out how to decrease in double knitting, you have to set the middle stitch (slipped st in 1 color dk, purled st in 2 color) aside (cable needle was suggested
now why didn't I think of that?), and k2tog. I
would then go ahead and p2tog, so I don't forget to decrease to match on the other side, but if you're doing 1color doubleknitting, this will close your tube!
I am not worried about it being able to open into a tube, I just want the double layers for softness. If you do this in 2color dk, make sure to purl the next 2tog in your 2nd color.
I got it!