I guess I will be a contrarian, or at least offer an alternate perspective. In fact, I will contradict my advice in a second post. There is no best answer but I hope this will encourage some thought.
I suggest you don't buy another lens. I suggest you wait. Why? Because you are happy with what you have and are enjoying your photography.
You are blissfully free of GAS!
The time to get the next lens is after you discover a photographic need and after going through the process of struggling with how best to fulfill that purpose. And wait till you have determined the best solution to your problem. This process will make you a better photographer because it will deepen your understanding.
For example, you might decide you want to photograph small things, which may lead you to a macro lens, although there are other methods.
Or you might have a hard time getting sharp enough images. This might lead you to a faster lens. Or it might lead you to the worlds sharpest lens (the old guys will know what I mean here
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What I would do instead of getting another lens before the desire was driving me to distraction, is to pretend my zoom is a prime and leave it set at one focal length and take all my pictures at that focal length.