- Gutermann A192 and Mara 150 are the same thickness
- You can't order onesie-twosie from Gutermann; and,
- not every retailer carries Mara 150.
Read the pamphlets. They tell you what needle size is recommended for each thickness of thread. It's in there. I'm not making this stuff up.
Also: go back to the Gutermann site. There's many other pamphlets about seam formation, quality and strength.