Talk to your pediatrician, but
1) I don't think whole milk is that hard to find.
2) If you can't find whole milk, 2% milk won't harm a 14 month old (unless he has some sort of milk allergy/intolerance anyhow)
3) You can start introducing cows milk at 12 months if pediatrician okays it, so you should know by 14 months if your child can tolerate it well.
All my babies have been small (even though they weren't preemies). My first son was 5lbs 3 oz, my twins were 5lbs 11 oz. and 6 lbs 11 oz. I breastfed all of them (the twins were supplemented with formula), so they had more of a breastfed growth curve, so they are still somewhat small.
With my first son, the doctor constantly got onto me about if I was making enough milk, adding oil to his food, making sure we did whole milk, etc., etc. He just gained slowly-he is still skinny. He is healthy at age 8 now. With my second two, the doctor seemed to pay much more attention to their growth curve than to make me worry all the time. He said I could have done lowfat milk starting at 12 months
With all that said, when we took a trip a week after my son turned 12 months old, I continued breastfeeding and gave him some formula (he had had formula mixed in his cereal/oatmeal before, so I knew he could handle it) because I didn't want to introduce something new while on vacation.