Many thanks to Zhen for recommending cushioned sandals, it feels like having little pillows to support our every step of walk, especially for people who love and must walk a lot like me.
While trying to understand more about the benefits and comfort that cushions bring (e.g. preventing and relieving the pains for corns, callous and bunions), I learn about cushioned gel made of transparent silicone. It comes with sticky pad. Ideally, it should be washable and reusable (eco-friendly!). Perhaps, next time I will try cushioned gel for my shoes / sandals / flip flops that are uncushioned.
I bought it at toa payoh for $10. I am grateful!