I got this http://www.amazon.co.uk/gp/product/B00B2PMAR8/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1.
I started using it at 10 weeks I think, it took a while to find the HB. You have to go slow and be patient. If you look up youtube for fetal heartbeat you can have a good idea of what to listen for. xx