Got mine a couple of years ago from Poundland and planted them among some David Austin Roses. This year they grew up to 1.5 meters tall x 1.2 wide. Don't plant them too deep, give them space, free draining soil, a bit of bone meal and you can't go wrong!
Every spring poundland have got a peony root for - you guessed it- £1!!! It's normally Sarah Bernhardt’ but I've seen other varieties in there too.
Ha. I agree I bought a run down cottage and renovated it. Had a lovely pink and white peony in the garden. I divided it and replanted some in my garden but for the life of my I can't get it to flower. The remains that were left scattered in the cottage garden are flourishing. the tenant keeps asking me to get rid of it as it is now a driveway. Too much clay in my garden I think
Postage is the killer, they also supply you with plants that are unlikely to flower next year and as mntioned are very temperamental taking a few years to get going
Peonies are also one of those temperamental plants that will prosper in some places but just turn up their toes a few feet away. You can never tell.