Do you have a tendency to lock your knees when you sing? Do you hips tuck forward or tilt back? You might look into a balance board.
The balance board ($20, Amazon) is a great multi-purpose tool for a singer. Use it to increase your strength and balance as intended as an exercise aid, or use it as you sing to reinforce balanced, free, aligned posture.
By destabilizing you, you body reacts by engaging muscles in the legs and core that support your posture, allowing other muscles in my abdomen to free to be used by your breath support mechanism. If your knees are locked, often your hips will shift their position to compensate, which forces your back muscles and abdominal muscles "to carry" your weight. Instead, we should absorb and support that weight with our feet and legs, allowing the hips to find their easy free alignment which then in turn frees our torso and breath,
This wooden balance board is nearly indestructible, small and inexpensive; it is a great choice for a singer or a teacher with many students but a small or traveling studio. The "next level" investment is the Bosu ball, which I will review in an upcoming video.