I have a TINY 2 lb. 8 month old male. He has a Puppia harness and I bought it from
www.bowsawowsa.com. They are on sale for 19.99 (USD). The harness is a little big around his chest, so I tightened it with an elastic until he grows a little more. Whatever you decide on, just make sure you measure your pup and then check the measurements with whatever harness you buy!