I rented a doppler my first pregnancy at 10.5 weeks, always found Baby's heartbeat quickly, and found it really reassuring - however I then found out at our 13 week scan that Baby was very ill with a condition that is not compatible with life and lost him a week later.
You'd think I wouldn't have wanted one for this pregnancy, but I still did and got it at 9.5 weeks this time. I couldn't find a heartbeat the first night I tried but found it the next morning in under 2 minutes and could always find it quickly after that. Even though I knew that finding a heartbeat is no guarantee of a positive outcome I still felt better going into my 12 week scan knowing that Baby was alive. Then I just had to worry about whether he was healthy, but one worry was easier to cope with than two.
I ended up with an anterior placenta so didn't feel movement until about 18 weeks, so I also found the doppler reassuring in that regard, because even when I couldn't feel him moving I could hear him crashing around on the doppler.
Just my experience and I know everyone's is different. I have a short torso and was fairly thin so that's probably why I could find Baby so easily so early on.
Whatever you decide on, I hope it brings you peace.