Hey Amy, I know this thread's a bit old now. Did you end up getting a doppler?
I got one around 14 weeks and for me, it's the best thing I ever bought! It's a Hi-bebe and I could find the hb quite easily at 14 weeks (and I have lots of belly fat!!) right down low at the pubic bone. There were a couple of times I couldn't find it early on but that was just due to inexperience. Within about a week, I could get it every time without fail and now can distinguish baby movement noises and everything! I really needed the reassurance because I had a subchorionic haemorrhage, then a UTI, then heart palpitations, then gastro. It was just so nice to be able to check that baby was ok, despite everything else. Now I really just use it occasionally, for fun