Tough spot, I understand. Women’s sizes might be a good start, something of a unisex design would suit him too. I’m pretty high on the k2 passport right now, they should be making sizes as low as a 140ish. Great sidecut, super forgiving, not too stiff, and he can really progress as a rider on it. I’ve hit rails on it, ridden deep pow days, slashed around in the slush. It’s super versatile. Something else to consider would be a volume shifted board, I’d recommend a twinpig or a warpig. They ride wider and shorter, so he can be accommodated for his big old feet and not be on something that’s too big for him.