Hello GardenerDan68.
To answer your technical breakdown for frothing milk without a dedicated tool, yes, a glass mason jar is the ideal vessel for this method.
For maximum aeration, you will want to shake the sealed jar vigorously for about 30 to 45 seconds until the volume nearly doubles.
After shaking, remove the lid entirely and microwave on high power for roughly 30 seconds in your 1200w unit to stabilize the protein structure.
Whole milk is significantly better than low-fat cultivars because the higher fat and protein content creates a stable microfoam that will not collapse quickly. Whole milk provides the consistency you are looking for.