How do you end up with a situation like this? Usually it's when you have feet of slightly different sizes. My guess is less than a half size difference. This actually is pretty common. In that case, the usual solution is to buy boots that fit the larger foot. (No one recommends buying boots to fit the smaller foot).
The other issue might be when you have one boot that stretches out a little faster than the other and feels a little too large. This isn't uncommon either. Maybe a skater uses one boot more heavily than the other due to sidedness or being a landing foot.
The third condition might be when buying boots you find that one size is too small and the half size up is too big.
There's no reason in these circumstances that you have to buy custom boots. In many cases, stock boots can be made to fit by a simple trick.
Put two insoles in the too large boots. This will push your foot up into the curve of the boot, and usually your boot will then fit (provided the 'too bigness' is limited).
You don't have to use thick insoles, in fact I don't think that's a good idea. I prefer doubling thin ones. You can then experiment with foam vs gel or even the nice leather ones.
Also don't waste your money on the expensive insoles. You can get thin insoles at the dollar store. These ought to do for your base insole, and you can put your superfeet or other expensive insoles on top.
The other advantage of using cheap thin insoles is you can cut them up and adjust the layering front and back to get just the right feel you want.
So there's your handy skating tip for the day.