Prior to my weight loss I wore a size 44I bra and now 32DD and I have consistently worn a Polar FT40 and LOVE it. The watch part and the snap on transmitter (snaps into the chest strap) both have batteries that you can change yourself (vs sending to the factory). The strap is machine washable, the unit is coded so as not to get signals from others.
I finally had to order a new, smaller strap to keep it fitting snugly. The strap has two spots that you get wet with water. You enter your age, weight, height, and gender and you can set it to tell you either heart rate or a percentage of your maximum heart rate. It also tells calories burned, which is primarily what I use it for.
Sorry I can't help with your Garmin. If it's that frustrating I'd try something else.