Besides all the other relevant advice (i.e., that a small neckdown won’t cause as bad localized heating as the formula suggests if it was on it’s own):
If you are milling the boards (no soldermask) - life is easy. Just coat high-power traces with solder and be done, don’t waste time getting fancy thicker copper boards etc. In fact I’ve seen the ‘add cross section to trace with solder’ technique used in real production boards too (some caveats here - see links with more details link one and link two.