MTB Sizing. Saddle at the very bottom to reach pedals perfectly. Go one size smaller?
If you have to put the saddle all the way down, the frame is too small large. You need to have a comfortable clearance between the top tube and your crotch when your feet are flat on the ground - especially on an off-road bike, since you'll often have to dismount in a hurry. There are other aspects to getting a proper fit, but this is something you can't get around.

Also, if you're on the short end of things, I wouldn't recommend a 29er. They do make them in small sizes, but in order to get a smaller rider into a reasonable riding position between those two big wheels, they have to make some compromises with the geometry. You'd be better off with 26" or 27.5" wheels.