Here is another alignment aid review for you!
I suffer from high arches and pronation. I have professionally made orthotics in my sneakers, but often the arch support in my day to day shoes is abysmal. Enter these guys, arch support pads!
You can buy these at Amazon for 6 bucks for 3 pairs right now. They are easy to clean and do their job; they add arch support to slippers, sandals and shows that lack them. But what on earth does this have to do with singing?
Your body alignment begins with your feet. You want your weight evenly distributed between your heel and the ball of the foot. I think of my foot as a tripod, with 2 points in the ball and 1 point in the heel, balanced equally. High arches that collapse, like mine, can through that balance off and cause the ankles to pronate (tilt in- supination is when they tilt out). There is a domino effect in the rest of my body; my knees lock, my hips sway and my torso and its muscles compensate.
Many, many singers suffer from poor arch support and don't even know it. The only reason I know I have high, collapsed arches and pronation is because I once sprained the bones in my feet ad went to a podiatrist that diagnosed me and created orthotics for me ($$$$). If you feel like you have been working on your own alignment and breath support for ages with no improvement, try out some of these arch supports. They are a very cheap investment, and might be the answer you are looking for!