Here's a way to bind off stitches that really helps your bind off stay loose. I "unvented" it while working through
Lynne Barr's mind-opening
Reversible Knitting. Captions are beneath the photos.

Here I have one stitch knit.

I put that stitch back onto the needle,

inserted my right needle through the next stitch as if to knit,

wrapped the yarn,

. . . and . . .

pulled the loop through both stitches.

Ta-daa!
This method helps keep the first stitch open. If you want extra insurance, you can hold it open with your thumb. I would use my left thumb to hold it open from the time I put it back onto the needle to the time I pulled the loop through both stitches.
Several stitch patterns in
Reversible Knitting call for passing slipped or worked stitches over other stitches. I find this method saves time, but I don't assume that would be the case for everyone. I just fling the stitch back onto the needle when I'm going in for my next stitch. Slick, if I do say so myself.