I'm the same size as you, and I just got a Polar HRM and have found it quite comfortable. In fact, sometimes I've forgotten I've had it on.

BTW, if you haven't already, check out the Enell sports bras. They are AMAZING but quite pricy. You won't need to wear two bras anymore. I started with the size 3, and now wear size 2 or 3 and will be replacing the size 3s as I go along.