It might be that you need to sit on it more like a cruiser style bike in a more upright position. That's how my wife's stationary bike is set up.
It has a much wider saddle similar to a cruiser style bike and the saddle is moved back so the pedals are further forward than they are on a road bike. The handle bars are toward the saddle and horizontal, but they aren't really used much as neither of us uses it for resistance training. So we can just sit upright and pedal fast enough to get our HR up.
Without the ability to tilt the saddle, you loose one thing that can make an otherwise uncomfortable saddle comfortable. Her stationary bike doesn't even allow saddles to be swapped easily. The mount is nothing like a bicycle saddle mount.