I recommend getting a lacrosse ball since they are quite cheap and versatile: https://www.amazon.com/Kieba-Massage-Lacrosse-Myofascial-Therapy/dp/B017V7UKW2/ref=sr_1_2?s=team-sports&ie=UTF8&qid=1486000450&sr=1-2

In addition, read up on trigger points and how to massage them. I suggest reading https://www.amazon.com/dp/B00ECLGALG/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1