The variety you are most likely to find in a garden centre is Munstead, a dwarf form. My own favourite is Imperial Gem, similar size, but IMHO a more eye catching deep purple colour. I first saw a field of it at Norfolk Lavender, and it looked wonderful. We bought 10 of them, and have propagated a lot more from it.
Yes I would make sure that the soil is well drained. It wil also help that the bed is raised. Lavenders that die in hard winters do so more because their roots have been stood in frozen water than because of damage to the stems.