Sizing varies from each designer/manufacturer so it is always best to measure your baby when ordering clothes. I know a lot of us here on YT can custom make clothes to fit measurements. Here is my website and I can do custom sizing if you would like:
www.tinkerbellscloset.com 
As for hair clips I personally prefer the little butterfly style clips as they are very easy to stick in the hair and they work great on my yorkie and you dont have to bother with rubberbands. I have several styles on my website (the clips Im talking about are the ones that come in pairs):
http://tinkerbellscloset.com/items/b...clips/list.htm