Could you recommend some exercise shoes for me?

I am going to be joining the gym at the YMCA soon. I am 47, way overweight and have weak ankles and flat feet. I will just be starting with walking mostly, but I still need a lot of support.

I haven’t bought a decent pair of gym shoes in ages. I can’t afford very much, but I thought maybe if I knew a good brand/kind, I could look for them second hand or something.

We have a boutique by us with shoes that were never used and are so much cheaper.