Which ones you buy will depend on a lot
First your age
If you are 5ft + and 38kg I asume you are still growing and going through that beanpole stage
If this is the case you will probably weigh 10kg more in a few months so I would go for the lightest adult ones you can get and sort of grow into them
If you are older and 38 kg is gonna be your weight for the forseeable future you may have some problems
One last thing I would weigh yourself in your normal clothes (the ones you will be bocking in) and shoes as this is the weight you should go by
Also I am no expert but if you are above 5 ft 36kg seems very light so I would say you could do with gaining a few kg just for health sake
Jason