The size of needles is picked mainly based on yarn thickness, that's true, but you need to understand that the numbers on Soviet needles and modern ones often don't match! I ran into this when I first wanted to just buy analogs of the old sizes - and almost messed up. The label always says which needles you need, go by that recommendation, it's universal.
As for the material - here's my advice! For a beginner (or someone getting back into it) I'd recommend metal, because it's easier to learn on them, stitches slide well and don't drop if you're not watching. Bamboo is cool, but stitches grip tighter on them, and that can be exhausting if you haven't gotten the hang of it yet. Plus bamboo needles make less noise - and that might seem like a plus, but sometimes you won't even hear that your knitting dropped right next to you!
The main thing people often forget - not all needles of the same size are equal! Different manufacturers can have slightly different sizes, and if your fabric turns out too tight at first, try going up half a size. Experiment right there in the store if you can, test them against the yarn you've already bought!