Autism

During my twenties I put in the work (years thereof, although some results came within months and I still keep in practice, among other things it's good for getting to sleep) and got a reasonable grasp of silence meditation. Generally this involved repeating a mantra for a while and then letting silence happen for as long as it would and then starting the mantra again, silence again, rinse, repeat.

It is hard for me to overstate how useful this has been for the rest of my life, I had intrusive, circular, exhausting thought patterns, now I can just will them to shut up. So peaceful. There are other benefits, but that seems the one most relevant to you. Key takeaway here is, it's like a muscle, you have to keep exercising it, and there's only so much you can do in any day that is helpful, indeed overdoing it, trying to make it happen faster, will just discourage and exhaust you, as it would injure a muscle, or it certainly did me. Just keep at it, to be cliche, it won't happen overnight, but it will happen (at least it did for me, and it's glorious).