How can I think in English, not my native language?

To speak English fluently, first, forget about the speaking part and just think in English. Get your internal voice talking in English. Laziness isn’t the issue. To do this doesn’t take hard work. It just takes repeated work. You can do it lazily and still get the same result. Actually, I’d recommend doing it lazily. When you are not busy, when you are not stressed, just think in English. The various parts of your brain are connected by neural pathways. As we do certain actions or think certain thoughts, electrical impulses travel along these pathways. The bigger pathways conduct the impulses faster and easier than the narrow pathways. When we learn something new, our brain actually builds new pathways between the various sections. We practice doing something, the pathways get larger and stronger. Repeating something often makes the brain faster at repeating that task in the future.

Two paths across a field. The left hand path is overgrown and bumpy, the right hand path is smooth and clear.

You can think of the pathways in your brain like the paths in the picture above. The right-hand path leads to your first language centre. The left-hand path leads to the second language centre. To improve your second language, you just need to walk on that path more often. As you do so, it will get wider and smoother, until both left and right paths look the same. However, I said walk, I didn’t say run. This isn’t hard exercise. Just wandering aimlessly and casually up and down the less worn path will build it up. There is no need to make it hard work.