Couldn't the countertop in the window recess be made "thinner" from below, so to speak? Do you understand what I mean?
A simple option would be niche material, which is not that thick, placed in the window recess. Then there would be a seam. Although seams on laminate countertops are relatively invisible. The only disadvantage would be that, depending on the material, a grain pattern, etc., would not continue seamlessly. Therefore, I would first try to pursue the "thinning method."
EDIT: And why are base height increases only possible in increments of 6 cm?