I am afraid I am to tight to buy seed potatoes. I just buy spuds from supermarket if I spot some I like, I put them on the kitchen table out of direct sunlight, wait for the black bits to show then plant. Always in bags but this year I will use some very large plant pots. 3 or 4 spuds in each. My own compost in the bottom half and bought compost on top. Don't use bags anymore despite having loads of them as they are cheap wilko ones and the handles rip off when I move them. The first lot I start in a greenhouse (double glazed and insulated roof. But they have to be removed before there ready as green fly hide in them. In fact they seem to attract them in the first place.