ditto on the 12 wt thread ... didn't know they made that! It must be like crochet cotton.
ditto on the needle size ... you need a bigger hole!
Another possibility could be the kind of thread re the fuzz problem. Some are notorious for that issue. Aurifil is a good one to avoid that ... though it looks like you haven't been able to sew enough to discover that!
Or the colour ... the darker the colour, the more dye, and the less consistency in the evenness of the thread.
Though I'd go with the needle change for the first and most likely solution!
I don't know what machine you are using, and don't know if all have this possibility ... Janome has a special bobbin case that saves the tension adjustment when working with different thread weights.
I hate adjusting tension ... so I'll go for anything that avoids that!
