Cut down the tall seat foam [w/electric knife-like the one used for carving Turkey] and recover. You could even cut a "step" into it that seems to be all the rage these days.
I have seen people try it and there is a guy here that can recover like no ones business. If I can find the foam I will be happier. A whole seat may make me happier yet.
The "parts interchange" chart on this site says that the KX seat foam will work [a little needs to be trimmed off the bottom, which should not be visible] and Ceet racing has them...
Not sure, but I am guessing that the 99-01 KX 125/250 model is what you will need. I have the same issue as you and your son, otherwise I would have offered up my spare seat ('01) for yours.
I was not suggesting that you go with a half assed look, I forget that not everyone enjoys fabricating/modifying stuff like I do.
Cool, I understand. I am a short guy myself, but my gasgas is a good 2" shorter than the rm250 I came from, so a tall seat will get me at the same seat height with some extra comfort. Rode a orange bike once with a tall soft seat and it was nice.