I buy organic potatoes for seed. I store them in the plastic bag in a dark place and after a couple weeks, they are ready to plant. Non-organic potatoes will work, but they take much longer to sprout.

You can also plant potatoes in the late fall and they will come up when they are ready. I have potatoes coming up in my front lawn 4 years after planting them. Unfortunately, the HOA didn't like the idea of a garden in the front lawn.

It looks like you are harvesting your potatoes too early. They don't start to develop well until they have flowers and then berries. I think 20 pounds is a good yield. You can get more by planting as deep as you can and then adding dirt as they grow. Some people put straw on top and they will grow under the straw.