ShiroKuro BartK I have setup overhead shots a couple of ways. One with a mic stand. The other using articulating arms attached to a wall shelf.
The tricky part to get a good overhead shot is the camera needs to be exactly over the center of the keyboard (so that the shot is square) and be high enough (to avoid distortion). Because my mic stand has limited lateral reach, it only works when positioned behind my DP. For grand piano, it looks to me the only viable position for mic stand is behind the bench. You need to be careful not bump into it when standing up. And it may become unsightly in wide shots. For the above reasons, I think a C stand (used for lighting) would work better. They are designed to be hold longer boom so you could place it to the side of the piano and still reach keyboard center.
Another method I have read about is to get a photography background support. It’s basically two stands connected by a long horizontal beam at the top. This would be the most stable way to mount a heavier camera like a DSLR. And this should be the easiest to adjust the camera to be perfect level. (On mic stand or C stand, using a mini-ball head to mount your camera/phone will make leveling the shot a lot easier).
In any case, setting up a good overhead host always take some back-and-forth tweaking. Therefore it’s best to do it once and leave it in place permanently.