The Yosemite bowline is just a simple bowline with a Yosemite finish. This finish can also be used with other knots, such as the figure 8. It is fail-proof for the figure 8 case, meaning that if you make it wrong the knot will compensate your mistake by tightening the rope on the correct spots. It is not fail-proof when used together with the bowline, as can be clear seen here (I don't agree with the title of this video, btw).
That said, one must keep in mind that you are a beginner. This is clear in the sentence
With both knots I am comfortable with omitting the stopper knot - because after several month of usage I never experienced the knots to get loose or untied.
Several months of usage is nothing in climbing. I have been climbing for many years and I have seen weird stuff happening that I would never, ever in my life considered possible. I have unclimped the top biner from a bolt while clipping the rope to the bottom one; I have tied in with a wrong knot, even though I have done it thousands of times before; I have seen a friend almost die because his jumar didn't bite the rope, and the list goes on. You have absolutely no idea of what awaits you with regards to fail-proof procedures simply failing! Your months of experience are not a parameter, and even if they were years or decades, you could still be wrong. Do not rely on anedoctal evidence, or you will eventually hurt yourself doing something completely avoidable.
When choosing a knot, I have always been in favor of choosing the best knot. For many years this was the figure 8 or a double bowline with a stopper knot. Nowadays, I don't believe this anymore. The EBSB knot is, according to my own personal view developed after several tests (some can be found here), the safest knot there is. However, if you are a beginner I would definitely recommend you sticking with the figure 8 for a while. The EBSB does not require a stopper knot, but I still almost always do one. However, I know that if I forget it, this is a knot with an extremely small probability of untying, as has been demonstrated several times.
Do not, ever, use a Yosemite finish without a stopper knot. You will probably die if the knot fails. Regarding the simple bowline, if gets loose quite easily without a stopper knot. Sometimes even a double bowline can get loose. If you do not like stopper knots, use a double bowline with an in-loop stopper knot, which you tie in the loop itself and doesn't bother you when pulling the rope to clip (if that's a problem for you). If you insist on not using a stopper knot, then use the EBSB bowline or a figure 8.