As for doppler--I am not sure I would be able to find anything. When the Dr does it I have no idea if it is me or if it is baby. I know there is a difference on how fast hb is compared to mine but I am honestly horrible with any elctronical devices. I think I would need to hire someone to do it for me if I bought a doppler.
YouTube! There are tons of tutorials that may help you. If you do decide to buy one, bring it to your Dr's office. I did and my OB was more than happy to let me feel (listen?) around with their doppler AND mine. At first I was totally useless, haha, but he took my hand and guided it to the HB. That was REALLY helpful because I could feel the right amount of pressure to bear down with, the best way to "sweep" to find the baby, etc.
So... Technically, you already HAVE hired someone to use a doppler.