Lavender, you can get a lot of different varieties that are different heights and flower at different times over spring. In my limited experience the older varieties seem a bit hardier with high winds (rather than the newer frilly ones) . They like good drainage so on top of a rise is better than at the bottom I think.

Borage has pretty blue star flowers in spring, it dies away for winter but self seeds a lot then pops up again.

Bees like these a lot.

Also African daisies are pretty hardy with wind, (though I dont think the bees like them much) I see them a lot on exposed places about, you can get purple ones not seen any blue though.

Globe thistles, im not sure how spreading they are though. but they are supposed to be hardy.

You can also get flower seed packets which might be good to sprinkle about to try- you can get them in blue colors/purple colors only.