My mind was blown when I found this little plastic ball in a sports store which you can put between your back and a wall and you can massage yourself. It works wonders within even seconds of using it. It's only a few euro and I used to waste hundreds of euro on massages. And you can take it anywhere because it's small and light.
My doctor prescribed me a lacrosse ball for a bad shoulder once, for exactly what you described. It’s slightly rubbery but really dense, and it’s apparently the perfect thing for tight muscles.