For reducing self-reflectiveness, mindfulness is not the most effective form of meditation. I suggest you try the following: It is super easy - although with your specific problem, it might be harder for you - so if it doesn't work you'll have wasted much less time than if mindfulness doesn't.

Your conscious mind has a limited cognitive capacity, and thoughts need it to run, which is why you can't have ten thoughts at the exact same time. This capacity is not reserved for reflective thought, which is why anger, for example, can use it up, to the point where you can't run self-reflection anymore.

Say you can have seven items in your working memory (very smart!), and it takes your working memory a seventeenth of a second to switch contents (very awake!) - that means you get 119 working memory contents per second. It is like bandwidth. The numbers vary, the principle doesn't. So all you need to do to starve your self-reflection of bandwidth is to flood your cognitive capacity with lots of items that are unrelated to reflection.

And that is really easy. All you need to do is look at something (or listen, if blind) and try to notice as many details as you can. I recommend looking at a tree and trying to see every single leaf like you would if you focused on a single one - but anything with some visual texture and no text on it works. If you want to keep it up for several minutes straight, I've found the key is to continually attempt to see even more details. Maybe that's because each of the details is kept as a seperate item, so they don't coalesce into self-perpetuating thoughts. Contents of working memory that don't self-perpetuate deteriorate quite quickly, and will be replaced with new ones - so you need to make sure they're again nonreflective perceptions.

Side effect: After a few minutes, this makes whatever you're looking at really fascinating and beautiful. This is because your brain uses the self-observation that it isn't experiencing distraction as a proxy for how important the thing you're not distracted from is.