my go to is always a blazer. if you are doing a solid dress you could get away with a fun striped blazer or a pattern. The other option would be a cardigan but I personally am not a fan, they hang funny on me.
To interact with clients - so more formality. But a stiff boring solid blazer kind of bores me.
This isn't something I typically wear so it's out of my comfort zone.
What do you typically wear?
Honestly - if you want more coverage you don't really have many options besides blazer or sweater...you could try a crisp white button-down underneath but I think that might look awkward in the back.
If coverage is not the issue so much as formality you could add a wide belt & coordinating pumps and some conservative jewelry (pearl studs, etc.).
Here's a Pin that shows all of my suggestions in one example lol:
I agree that this dress is perfectly professional all on its own, but I think you are limited to a jacket or blazer or cardigan.
That said, you have so many options other than a "boring solid blazer".
Ann Taylor's site alone has many options:
Any of those jackets break the boring blazer mold and can add a pop of color or style to the dress. I love the dress! Take it with you to a Nordstrom or even an Ann Taylor store and ask a sales person to help you find something to go with it.
And make sure you post pics once you settle on something.