Have you considered pencil skirt dresses, like the one shared by a previous poster from The Pretty Dress Company? They give you some tailoring, which you need when going in for a senior position, but without wearing a full suit. Closet London has quite a few with varying sleeve lengths in your price range (some are too bridesmaid or holiday or casual, but quite a few are office appropriate, like:
https://closetlondon.com/closet-london-purple-v-neck-midi-pencil-dress/
(It comes in your size and is viscose, nylon, and a small part elastane, so it will have some give)
So do The Pretty Dress Company, ASOS, and many others. Some of the previous dresses shared are very nice, but you cannot go to a senior management interview in a jersey dress from Boden or something midi with tiers. It’s simply too casual (In fact, the only even vaguely appropriate dresses on Boden were still pencil skirt dresses).
And I think you might easily find a dress under £80, especially in the sales.
I admit, however, if it is a super casual company (tech or start up or something), perhaps some of these lovely, though casual, choices would be just fine.
Also, whilst some of the dresses recommended are truly beautiful, like the Love and Roses one, which is definitely not too casual, they are quite romantic-feminine. Which is fine as a style to wear to the office. But for your initial interview, usually a solid color is recommended; you want their first thought of you to be “management potential,” not your dress fabric. Same reason men interviewing for senior positions wear solid-colored ties and not busy floral ones.
Good luck! I do hope you find the right dress that makes you feel supremely confident, and that your interview goes well!!!