Definitely go with just the bar for awhile. Make sure you are centering yourself on the bar, as well. I’m always amazed when I see someone squatting with the bar a couple inches off-center, and they just gut through it like it’s supposed to do that.
If your worried about not getting the work in, do a few sets of just the bar, then follow up with DB squats maybe to get the work in.
Also, are you squatting in running shoes? The extra cushion in the heels can cause instability, though I’ve never seen it in that light a weight. But as you said, you are a beginner so that may be part of it. Get some Chuck Taylor’s, or some Adidas Sambas(what I use).
They are flat soled, as well as thin soled, which will provide a more stable base. If you can’t get some, or don’t want to spend the money, just squat barefoot. Works just as well.
Lot’s of good advice from the other posts here as well. Good on ya for wanting to stick with the squats even though they are hard. Most people won’t even try them cause they’re ‘dangerous’.