Hi hon I think it's only understandable that you'd be feeling nervous with everything you're going through ATM. Never had the need for a doppler myself but the one comment I have heard several times over is that unless you really know what you're doing with them they can induce more worry than if you never had one. I think sometimes for the un-experienced hand it can still be difficult to find a HB depending on how bubs is lying. Still, if you think it's a good move and will bring you reassurance, go for it! If you're not entirely sure though I reckon your Doctor would surely prescribe extra scans periodically to ease your mind, especially in light of your circumstances.