After doing a ton of research on what causes the thread to bind up and how to stop fabric from getting dragged into the machine, I was hoping I'd have some good news. I don't.
At least, not 100%.
The good news is that I had a few things set wrong on my machine. Upper-thread and lower thread tension is important. I didn't know proper bobbin tension tests, because the machine I learned on was the Husqvarna Viking, which does away with the bobbin-case, so I didn't have to worry about the bobbin tension. I also needed an upper thread tension of about 5. That solved the jamming.
It was suggested that I put tissue paper under the fabric to get it started, to prevent it from getting dragged into the machine. This means sewing the tissue paper into the garment, but it can easily be ripped out, and I already had some tissue paper laying around for other projects a year or two ago. It works.
The bad news...
Part of this requires me to do a zigzag stitch, which is a type of stretch stitch, which is why straight-stitch plates wouldn't work.
I ended up getting half way through my first seam before realizing every other stitch was being skipped by the machine. The thread would go in on the right just fine, but when it would switch to do the left stitch, the thread would come back out, every single time. So I ended up with a straight stitch and an extremely puckered seam.
According to a little more research, I have to either try a larger needle, or I have to get a stretch needle. I found out what a stretch needle is, finally. It's a ballpoint needle that's designed a little differently, specifically to avoid skipped stitches.
Fuck my life.
Life Advice: Never listen to the professionals. They never have a clue in fucking hell what they're talking about. Retards, every single last one of them. 10 different god damn "professionals" assured me "You need a jersey needle, you need a jersey needle, you need a jersey needle." Which is the official term for regular ballpoint needles. Not a single one of those bastards mentioned a stretch needle. No, I had to find out about those on a hobbyist blog.
I'm very quickly running out of patience. If I can't figure this out, I'm moving on with plain clothes from the Goodwill/Salvation Army, and I'll finish the god damn unitard version when I can afford to drop $400+ on a faggot serger.
Back to the store again. Hopefully I don't get another sunburn.
Update: I don't know why I keep going to Walmart. Ever since the smaller ones closed down in favor of the larger ones, the store has gone straight to hell.
I think it goes without saying that they didn't have what I need. I'm never going there again. I got lucky, one time, in a moment of desperation, but that's once in a 5 year streak I've left that store and not been disappointed.
Update 2: Found some on Amazon that aren't Add-On items. Only problem is that they won't arrive until June. So I won't know until then whether this is a waste of money or not.