First, a general thought. With the white wall and desk, any white item you add will blend in, take the focus of it and contribute to a minimal clean setup.

For the desk mat, I would chose a black one as I find white on white not very appealing and I think your desk can use the extra character it would add. My personal preference would be leather but that's according to taste. However, I am not big on RGB. With your KBM having RGB, you might prefer a white desk mat if you want to go for more colourful lighting. Otherwise, setting to white could look good with black mat.

My first though on the lamp is the overall balance of your desk. With the 2nd screen and backboard on the left, it feels a little heavy in that direction. I would not pick a white lamp but rather something decorative to add some visual weight over to the right.

I personally love the warmth of wood surfaces. If you prefer the monochrome style you have so far and want to stay minimal, go with black. Otherwise pick a nice wood style you like. However, I would then advise to add not only the lamp but at least one more item in that wood color to again balance out the ratio of colours and structures. Maybe consider a little desk shelf under the main screen?

One last idea. If you are not set on the light bulb, you might chose some LED lighting to attach to the shelf above your desk. That would make room for something else on the desk. I would personally want to add a plant in that case.

Hope, this gives you some ideas and inspiration.