Nothing compact about 'Grosso' - in fact, it is a larger growing hybrid and is often used as a hedging plant. And won't be as hardy for you as any of the English lavenders (Lavandula angustifolia).

Some of the best dwarf/compact lavenders are some of the oldest selections - 'Hidcote' and 'Munstead'. Other good choices are 'Blue Cushion', 'Twickle Purple', 'Folgate' and 'Sachet'.

Yup,I realized I had mistyped too late (re "Grosso') and of course there is no period of grace for editing.

I have easy access to 'Blue Cushion'. I am glad you mentioned this in your post.