Yes you are dead right, hardy plumbago. I would go for Ceratostigma griffithii which forms a sizeable shrub. Ceratostigma plumbaginoides is a herbaceous perennial who's leaves turn red or purple in autumn. But beware, it spreads underground and can be very invasive. I've just finished digging it up!

I have Ceratostigma griffithii which I purne lightly but the Ceratostigma plumbaginoides I have potted up and given to a couple of neighbours but with the warning.

Ceratostigma, very pretty. I've got one Siris sent me a root of a few years ago and it's coming into flower now. I keep it in a pot.

Sorry I'm late to reading these replies. All more than helpful.

We had C. wilmottianum which has an award of merit as a garden plant. Paler blue than the one shown.

Mine are C. willmottianum too … not only a pretty flower, but lovely autumn leaf colour as well.

We also have a pink flowered version as well.