I use a Groz-Beckert #18 and I have a Tin Lizzy. I use King Tut thread in the top and most time Superior So Fine in the bobbin. Here is a link from Superior Threads that may be useful. I hope you get your problem figured out, thread breakage is no fun.
https://www.superiorthreads.com/prod...chine-needles/
Good Luck
T