What is the best way to sew knit/stretchy fabrics? I’ve done my research and actually tried some of them but the end results are the same: wonky.

I’m using needles specifically for knit fabrics, I have used a knit foot. I have tried adjusting the tension…I have also tried placing a paper underneath the fabric. They all failed.

I have ordered a walking foot online so I’ve yet to try that route.

So for the meantime, I thought I’d ask here.
I would suggest iron-on soluble interfacing. That should keep the fabric stiff enough that it won't stretch while sewing (and suggested to use zig-zag stitch if using really stretchy stuff like spandex). When you're done sewing, just wash it and it'll dissolve in the water.