I have this problem although I'm still feeding (over 4 years so far) and will be for a while yet I think (youngest is 15mo), both favoured the left so it is now substantially bigger. I'm really hoping they will even out someday, although I'm getting worried as DD2 has started feeding mostly from the right side but neither seemed to alter size (I did get a blocked duct and bout of mastitis though in the process lol).

I just fit to the larger one. I find t-shirt style bras (full cup type) the best, so the cup has a lot of coverage which seems to make it much much harder for the little one to fall out the gaping top when bending over if that makes sense.