The idea of a nursery bed is a good one. I have a nursery bed in my vegetable garden. The reason sea lavender does not like to be transplanted is that the roots are long and easily damaged. Plant it in a cheap pot with good drainage and enough room for the roots and sink the pot up to 1/2 an inch from the top into the ground of your nursery bed and leave it until next spring. When the soil is warm enough to plant dig up the pot and really soak the soil in it so the roots will release from the sides and bottom of the plant. This way you do minimum damage to the roots. Then plant it in it's permanent place. I like to put water in my planting hole and let it soak into the ground so the roots hit moist soil right away.

Establish does not mean the plant won't be big enough. It means it takes that long for it to make where it's planted it's home and it probably won't flower until then but you will have the greenery so it shouldn't look out of place in your border

Brilliant!!! I really appreciate the details too.